iflib: Prevent watchdog from resetting idle queues

While changing link state in iflib_link_state_change(), queues are
marked as IFLIB_QUEUE_IDLE to disable watchdog. Currently, iflib_timer()
watchdog does not check for previous queue status before marking it as
IFLIB_QUEUE_HUNG.

This patch adds check of queue status before marking it as hung.

Signed-off-by: Piotr Pietruszewski <piotr.pietruszewski@intel.com>

PR: 239240
Submitted by: Piotr Pietruszewski <piotr.pietruszewski@intel.com>
Reported by: ultima@
Reviewed by: gallatin@, erj@
MFC after: 3 days
Sponsored by: Intel Corporation
Differential Revision: https://reviews.freebsd.org/D21712