community/keepalived: build with nftables support

Enable nftables support so keepalived can enforce VRRP no_accept mode
and properly handle VMAC multicast filtering. Without firewall support
(nftables or iptables), these features are non-functional, leading to
incorrect traffic acceptance on BACKUP nodes and improper multicast
behavior.

This is enabled by default if libnftnl is found. I think that it was
disabled by accident, not intentionally.

This change increases keepalived size by 32 kiB and add dependency on
libnftnl (180 kiB) and libmnl (40 kiB).

community/keepalived/APKBUILD

@@ -13,6 +13,7 @@ makedepends="
 	autoconf
 	automake
 	libnfnetlink-dev
+	libnftnl-dev
 	libnl3-dev
 	linux-headers
 	net-snmp-dev