ipvs: only unlock in ip_vs_edit_service() if already locked

Jumping to out unlocks __ip_vs_svc_lock, but that lock is not taken until
after code that may jump to out.

This problem was detected by sparse.

make C=1
  CHECK   net/ipv4/ipvs/ip_vs_ctl.c
net/ipv4/ipvs/ip_vs_ctl.c:1332:2: warning: context imbalance in 'ip_vs_edit_service' - unexpected unlock

Acked-by: Sven Wegener <sven.wegener@stealer.net>
Acked-by: Julius Volz <juliusv@google.com>
Signed-off-by: Simon Horman <horms@verge.net.au>