If tgt_net is set based on IFA_TARGET_NETNSID attribute in the dump
request, make sure all error paths call put_net.

Fixes: 5fcd266a ("net/ipv4: Add support for dumping addresses for a specific device")
Fixes: c33078e3 ("net/ipv4: Update inet_dump_ifaddr for strict data checking")
Reported-by: Li RongQing <lirongqing@baidu.com>
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>