Add OsConstants NETLINK_NETFILTER to public API

Tethering use NETLINK_NETFILTER to update NAT conntrack entry
for tethering offload. Netlink netfilter socket is protected by SELinux
that only system_server, netd and networkStack(tethering) may use it.

Bug: 144814535
Test: build
Change-Id: Idf76ea546229790a407b69ba44f51c8a60d38abf
2 files changed