libceph: resend lingering requests with a new tid

Both not yet registered (r_linger && list_empty(&r_linger_item)) and
registered linger requests should use the new tid on resend to avoid
the dup op detection logic on the OSDs, yet we were doing this only for
"registered" case.  Factor out and simplify the "registered" logic and
use the new helper for "not registered" case as well.

Fixes: http://tracker.ceph.com/issues/8806

Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Alex Elder <elder@linaro.org>