tipc: fix the error handling in tipc_udp_enable()

Fix to return a negative error code in enable_mcast() error handling
case, and release udp socket when necessary.

Fixes: d0f91938 ("tipc: add ip/udp media type")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>