Build-Fix

Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>
diff --git a/net/mptcp/mptcp_input.c b/net/mptcp/mptcp_input.c
index 968260e..f04a3f1 100644
--- a/net/mptcp/mptcp_input.c
+++ b/net/mptcp/mptcp_input.c
@@ -1365,12 +1365,9 @@
 	}
 	case MPTCP_SUB_ADD_ADDR:
 	{
+#if IS_ENABLED(CONFIG_IPV6)
 		struct mp_add_addr *mpadd = (struct mp_add_addr *)ptr;
 
-		if (!mopt->mpcb)
-			break;
-
-#if IS_ENABLED(CONFIG_IPV6)
 		if ((mpadd->ipver == 4 && opsize != MPTCP_SUB_LEN_ADD_ADDR4 &&
 		     opsize != MPTCP_SUB_LEN_ADD_ADDR4 + 2) ||
 		    (mpadd->ipver == 6 && opsize != MPTCP_SUB_LEN_ADD_ADDR6 &&