[openwrt/openwrt] netfilter.mk: add version conditional for nf_nat_ipv4, 6

[LEDE Commits]

yousong pushed a commit to openwrt/openwrt.git, branch master:
https://git.openwrt.org/a5c10ba9809454226fea6dda175150bc17e793d5

commit a5c10ba9809454226fea6dda175150bc17e793d5
Author: Yousong Zhou <yszhou4tech at gmail.com>
AuthorDate: Fri Sep 25 22:37:43 2020 +0800

    netfilter.mk: add version conditional for nf_nat_ipv4,6
    
    The upstream linux commit is 3bf195ae ("netfilter: nat: merge
    nf_nat_ipv4,6 into nat core").  It was included since linux 5.1
    
    Signed-off-by: Yousong Zhou <yszhou4tech at gmail.com>
---
 include/netfilter.mk | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/netfilter.mk b/include/netfilter.mk
index 9f22512d68..3c217db106 100644
--- a/include/netfilter.mk
+++ b/include/netfilter.mk
@@ -185,8 +185,8 @@ $(eval $(call nf_add,IPT_IPV6_EXTRA,CONFIG_IP6_NF_MATCH_RT, $(P_V6)ip6t_rt))
 # kernel only
 $(eval $(if $(NF_KMOD),$(call nf_add,NF_NAT,CONFIG_NF_NAT, $(P_XT)nf_nat),))
 $(eval $(if $(NF_KMOD),$(call nf_add,NF_NAT,CONFIG_NF_NAT_REDIRECT, $(P_XT)nf_nat_redirect),))
-$(eval $(if $(NF_KMOD),$(call nf_add,NF_NAT,CONFIG_NF_NAT_IPV4, $(P_V4)nf_nat_ipv4),))
-$(eval $(if $(NF_KMOD),$(call nf_add,NF_NAT6,CONFIG_NF_NAT_IPV6, $(P_V6)nf_nat_ipv6),))
+$(eval $(if $(NF_KMOD),$(call nf_add,NF_NAT,CONFIG_NF_NAT_IPV4, $(P_V4)nf_nat_ipv4, lt 5.1)))
+$(eval $(if $(NF_KMOD),$(call nf_add,NF_NAT6,CONFIG_NF_NAT_IPV6, $(P_V6)nf_nat_ipv6, lt 5.1)))
 
 $(eval $(if $(NF_KMOD),$(call nf_add,IPT_NAT,CONFIG_NETFILTER_XT_NAT, $(P_XT)xt_nat),))
 $(eval $(if $(NF_KMOD),$(call nf_add,IPT_NAT,CONFIG_IP_NF_NAT, $(P_V4)iptable_nat),))