libceph: don't omit recovery_deletes in target_copy()

Currently target_copy() is used only for sending linger pings, so
this doesn't come up, but generally omitting recovery_deletes can
result in unneeded resends (force_resend in calc_target()).

Fixes: ae78dd81

 ("libceph: make RECOVERY_DELETES feature create a new interval")
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>