Do not take a copy of the SSL context

When SSL certificates are renewed during runtime (via SIGUSR2),
e->dtls_ctx is replaced with a context based on the new certificate.
But this code continues to operate on its own borrowed pointer.

This is clearly visible using valgrind, but the bug is subtle and not
always noticed at runtime, possibly due to some fortunate re-use of
memory.

At the point of SSL_new():

==28413== Thread 5:
==28413== Invalid read of size 8
==28413==    at 0x4F6198F: SSL_new (in /lib/libssl.so.1.1)
==28413==    by 0x137A72: dtls_server_input_handler (dtls_listener.c:291)
==28413==    by 0x137A72: handle_udp_packet (dtls_listener.c:443)
==28413==    by 0x138153: udp_server_input_handler (dtls_listener.c:728)
==28413==    by 0x4FC499E: ??? (in /usr/lib/libevent_core-2.1.so.7.0.0)
==28413==    by 0x4FC50AF: event_base_loop (in /usr/lib/libevent_core-2.1.so.7.0.0)
==28413==    by 0x121F34: run_events (netengine.c:1579)
==28413==    by 0x121F34: run_general_relay_thread (netengine.c:1707)
==28413==    by 0x40517B6: start (pthread_create.c:195)
==28413==    by 0x40538EF: ??? (clone.s:22)
==28413==  Address 0x49a75e0 is 0 bytes inside a block of size 1,024 free'd
==28413==    at 0x48A074F: free (vg_replace_malloc.c:540)
==28413==    by 0x4F5F6F1: SSL_CTX_free (in /lib/libssl.so.1.1)
==28413==    by 0x11CEC4: set_ctx (mainrelay.c:3104)
==28413==    by 0x11D233: openssl_load_certificates (mainrelay.c:3173)
==28413==    by 0x11D328: reload_ssl_certs (mainrelay.c:3190)
==28413==    by 0x4FC4601: ??? (in /usr/lib/libevent_core-2.1.so.7.0.0)
==28413==    by 0x4FC50AF: event_base_loop (in /usr/lib/libevent_core-2.1.so.7.0.0)
==28413==    by 0x122582: run_events (netengine.c:1579)
==28413==    by 0x122582: run_listener_server (netengine.c:1603)
==28413==    by 0x110BB8: main (mainrelay.c:2536)
==28413==  Block was alloc'd at
==28413==    at 0x489F72A: malloc (vg_replace_malloc.c:309)
==28413==    by 0x4DFA2C6: CRYPTO_zalloc (in /lib/libcrypto.so.1.1)
==28413==    by 0x4F5F79E: SSL_CTX_new (in /lib/libssl.so.1.1)
==28413==    by 0x11CA80: set_ctx (mainrelay.c:2875)
==28413==    by 0x11D233: openssl_load_certificates (mainrelay.c:3173)
==28413==    by 0x110A19: openssl_setup (mainrelay.c:3139)
==28413==    by 0x110A19: main (mainrelay.c:2396)
==28413==

src/apps/relay/dtls_listener.c

@@ -55,12 +55,6 @@ struct dtls_listener_relay_server_info {
   ioa_engine_handle e;
   turn_turnserver *ts;
   int verbose;
-#if DTLS_SUPPORTED
-  SSL_CTX *dtls_ctx;
-#if DTLSv1_2_SUPPORTED
-  SSL_CTX *dtls_ctx_v1_2;
-#endif
-#endif
   struct event *udp_listen_ev;
   ioa_socket_handle udp_listen_s;
   ur_addr_map *children_ss; /* map of socket children on remote addr */
@@ -288,13 +282,13 @@ static ioa_socket_handle dtls_server_input_handler(dtls_listener_relay_server_ty
 #if DTLSv1_2_SUPPORTED
 	if(get_dtls_version(ioa_network_buffer_data(nbh),
 							(int)ioa_network_buffer_get_size(nbh)) == 1) {
-		connecting_ssl = SSL_new(server->dtls_ctx_v1_2);
+		connecting_ssl = SSL_new(server->e->dtls_ctx_v1_2);
 	} else {
-		connecting_ssl = SSL_new(server->dtls_ctx);
+		connecting_ssl = SSL_new(server->e->dtls_ctx);
 	}
 #else
 	{
-		connecting_ssl = SSL_new(server->dtls_ctx);
+		connecting_ssl = SSL_new(server->e->dtls_ctx);
 	}
 #endif
 
@@ -573,13 +567,13 @@ static int create_new_connected_udp_socket(
 #if DTLSv1_2_SUPPORTED
 		if(get_dtls_version(ioa_network_buffer_data(server->sm.m.sm.nd.nbh),
 							(int)ioa_network_buffer_get_size(server->sm.m.sm.nd.nbh)) == 1) {
-			connecting_ssl = SSL_new(server->dtls_ctx_v1_2);
+			connecting_ssl = SSL_new(server->e->dtls_ctx_v1_2);
 		} else {
-			connecting_ssl = SSL_new(server->dtls_ctx);
+			connecting_ssl = SSL_new(server->e->dtls_ctx);
 		}
 #else
 		{
-			connecting_ssl = SSL_new(server->dtls_ctx);
+			connecting_ssl = SSL_new(server->e->dtls_ctx);
 		}
 #endif
 
@@ -912,14 +906,6 @@ static int init_server(dtls_listener_relay_server_type* server,
 
   if(!server) return -1;
 
-#if DTLS_SUPPORTED
-  server->dtls_ctx = e->dtls_ctx;
-
-#if DTLSv1_2_SUPPORTED
-  server->dtls_ctx_v1_2 = e->dtls_ctx_v1_2;
-#endif
-#endif
-
   server->ts = ts;
   server->connect_cb = send_socket;