gre: use alternative way to check if kernel support is enabled

When necessary support is built in kernel, gre protocol support is
not enabled in netifd.

Signed-off-by: Alin Nastac <[email protected]>

package/network/config/gre/Makefile

@@ -8,7 +8,7 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=gre
-PKG_RELEASE:=12
+PKG_RELEASE:=13
 PKG_LICENSE:=GPL-2.0
 
 include $(INCLUDE_DIR)/package.mk

package/network/config/gre/files/gre.sh

@@ -291,8 +291,6 @@ proto_grev6tap_init_config() {
 }
 
 [ -n "$INCLUDE_ONLY" ] || {
-	[ -f /lib/modules/$(uname -r)/gre.ko ] && add_protocol gre
-	[ -f /lib/modules/$(uname -r)/gre.ko ] && add_protocol gretap
-	[ -f /lib/modules/$(uname -r)/ip6_gre.ko ] && add_protocol grev6
-	[ -f /lib/modules/$(uname -r)/ip6_gre.ko ] && add_protocol grev6tap
+	[ -d /sys/module/ip_gre ] && { add_protocol gre; add_protocol gretap; }
+	[ -d /sys/module/ip6_gre ] && { add_protocol grev6; add_protocol grev6tap; }
 }