[TCP]: Fix oops caused by tcp_v4_md5_do_del

md5sig_info.alloced4 must be set to zero when freeing keys4, otherwise
it will not be alloc'd again when another key is added to the same
socket by tcp_v4_md5_do_add.
Signed-off-by: NLeigh Brown <leigh@solinno.co.uk>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp_ipv4.c

@@ -928,6 +928,7 @@ int tcp_v4_md5_do_del(struct sock *sk, __be32 addr)
 			if (tp->md5sig_info->entries4 == 0) {
 				kfree(tp->md5sig_info->keys4);
 				tp->md5sig_info->keys4 = NULL;
+				tp->md5sig_info->alloced4 = 0;
 			} else if (tp->md5sig_info->entries4 != i) {
 				/* Need to do some manipulation */
 				memcpy(&tp->md5sig_info->keys4[i],