strongswan: fix connmark plugin dependency

The connmark plugin does not require the iptables binary, it uses
libiptc instead.

Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>
(cherry picked from commit 6cb15df69a)

net/strongswan/Makefile

@@ -670,7 +670,7 @@ $(eval $(call BuildPlugin,blowfish,Blowfish crypto,))
 $(eval $(call BuildPlugin,ccm,CCM AEAD wrapper crypto,))
 $(eval $(call BuildPlugin,chapoly,ChaCha20-Poly1305 AEAD crypto,))
 $(eval $(call BuildPlugin,cmac,CMAC crypto,))
-$(eval $(call BuildPlugin,connmark,netfilter connection marking,+iptables-legacy))
+$(eval $(call BuildPlugin,connmark,netfilter connection marking,+libip4tc))
 $(eval $(call BuildPlugin,constraints,advanced X509 constraint checking,))
 $(eval $(call BuildPlugin,coupling,IKEv2 plugin to couple peer certificates permanently to authentication,))
 $(eval $(call BuildPlugin,ctr,Counter Mode wrapper crypto,))