ss: Identify more netlink protocol names

There were only few Netlink protocol names
which were printed on the screen:

    rtnl, fw, tcpdiag

So added the ability to identify Netlink proto name
from /etc/iproute/nl_protos or from static table.

Signed-off-by: Vadim Kochan <vadim4j@gmail.com>
diff --git a/include/rt_names.h b/include/rt_names.h
index 56b649a..c0ea4f9 100644
--- a/include/rt_names.h
+++ b/include/rt_names.h
@@ -29,5 +29,7 @@
 const char * ll_proto_n2a(unsigned short id, char *buf, int len);
 int ll_proto_a2n(unsigned short *id, const char *buf);
 
+const char *nl_proto_n2a(int id, char *buf, int len);
+int nl_proto_a2n(__u32 *id, const char *arg);
 
 #endif