sctp: fix warning when compiling without IPv6

net/sctp/protocol.c: In function ‘sctp_addr_wq_timeout_handler’:
net/sctp/protocol.c:676: warning: label ‘free_next’ defined but not used
Signed-off-by: Daniel Halperin <dhalperi@cs.washington.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/protocol.c

@@ -673,7 +673,9 @@ void sctp_addr_wq_timeout_handler(unsigned long arg)
 				SCTP_DEBUG_PRINTK("sctp_addrwq_timo_handler: sctp_asconf_mgmt failed\n");
 			sctp_bh_unlock_sock(sk);
 		}
+#if IS_ENABLED(CONFIG_IPV6)
 free_next:
+#endif
 		list_del(&addrw->list);
 		kfree(addrw);
 	}