socket: fix set not used warning

The variable owned_by_user is always set, but only used
when kernel is configured with LOCKDEP enabled.

Get rid of the warning by moving the code to put the call
to owned_by_user into the the rcu_protected call.

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>