tipc: fix possible memory leak in tipc_udp_enable()

'ub' is malloced in tipc_udp_enable() and should be freed before
leaving from the error handling cases, otherwise it will cause
memory leak.

Fixes: ba5aa84a ("tipc: split UDP nl address parsing")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>