libceph: use target_copy() in send_linger()

Instead of copying just oloc, oid and flags, copy the entire
linger target.  This is more for consistency than anything else,
as send_linger() -> submit_request() -> __submit_request() sends
the request regardless of what calc_target() says (i.e. both on
CALC_TARGET_NO_ACTION and CALC_TARGET_NEED_RESEND).

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>