net: tipc: prevent possible null deref of link

`tipc_node_apply_property` does a null check on a `tipc_link_entry`
pointer but also accesses the same pointer out of the null check block.

This triggers a warning on Coverity Static Analyzer because we're
implying that `e->link` can BE null.

Move "Update MTU for node link entry" line into if block to make sure
that we're not in a state that `e->link` is null.
Signed-off-by: Cengiz Can <cengiz@kernel.wtf>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/node.c

@@ -2181,9 +2181,11 @@ void tipc_node_apply_property(struct net *net, struct tipc_bearer *b,
 							&xmitq);
 			else if (prop == TIPC_NLA_PROP_MTU)
 				tipc_link_set_mtu(e->link, b->mtu);
+
+			/* Update MTU for node link entry */
+			e->mtu = tipc_link_mss(e->link);
 		}
-		/* Update MTU for node link entry */
-		e->mtu = tipc_link_mss(e->link);
+
 		tipc_node_write_unlock(n);
 		tipc_bearer_xmit(net, bearer_id, &xmitq, &e->maddr, NULL);
 	}