netfilter.mk: add version conditional around CONFIG_NF_NAT_PROTO_GRE

It was removed in upstream linux commit faec18db ("netfilter: nat:
remove l4proto->manip_pkt").  This happened since linux 5.0

Signed-off-by: Yousong Zhou <[email protected]>

include/netfilter.mk

@@ -220,7 +220,7 @@ $(eval $(call nf_add,NF_NATHELPER_EXTRA,CONFIG_NF_CONNTRACK_BROADCAST, $(P_XT)nf
 $(eval $(call nf_add,NF_NATHELPER_EXTRA,CONFIG_NF_CONNTRACK_AMANDA, $(P_XT)nf_conntrack_amanda))
 $(eval $(call nf_add,NF_NATHELPER_EXTRA,CONFIG_NF_NAT_AMANDA, $(P_XT)nf_nat_amanda))
 $(eval $(call nf_add,NF_NATHELPER_EXTRA,CONFIG_NF_CT_PROTO_GRE, $(P_XT)nf_conntrack_proto_gre, lt 5.1))
-$(eval $(call nf_add,NF_NATHELPER_EXTRA,CONFIG_NF_NAT_PROTO_GRE, $(P_V4)nf_nat_proto_gre))
+$(eval $(call nf_add,NF_NATHELPER_EXTRA,CONFIG_NF_NAT_PROTO_GRE, $(P_V4)nf_nat_proto_gre, lt 5.0))
 $(eval $(call nf_add,NF_NATHELPER_EXTRA,CONFIG_NF_CONNTRACK_H323, $(P_XT)nf_conntrack_h323))
 $(eval $(call nf_add,NF_NATHELPER_EXTRA,CONFIG_NF_NAT_H323, $(P_V4)nf_nat_h323))
 $(eval $(call nf_add,NF_NATHELPER_EXTRA,CONFIG_NF_CONNTRACK_PPTP, $(P_XT)nf_conntrack_pptp))