cxgbe: fix LINT-NOIP builds

The -NOIP builds fail because cxgbe_tls_tag_free() has no prototype (if
neither INET nor INET6 are defined). The function isn't actually used
in that case, so we can just remove the stub implementation.

Sponsored by:	Rubicon Communications, LLC ("Netgate")

sys/dev/cxgbe/crypto/t4_kern_tls.c

@@ -2138,12 +2138,6 @@ t6_ktls_write_wr(struct sge_txq *txq, void *dst, struct mbuf *m, u_int nsegs,
 	panic("can't happen");
 }
 
-void
-cxgbe_tls_tag_free(struct m_snd_tag *mst)
-{
-	panic("can't happen");
-}
-
 void
 t6_ktls_modload(void)
 {