ix(4): Move {mod,msf,mbx,fdir,phy,link}_task to lock protected handler

This patch introduces adapter->task_requests register responsible for recording
requests for mod_task, msf_task, mbx_task, fdir_task, phy_task and link_task
calls. Instead of enqueueing each of these tasks with GROUPTASK_ENQUEUE, new
task is created and all handlers are called from one task while holding
adapter->core_mtx lock.

SIOCGIFXMEDIA ioctl() call reads adapter->media list. The list is deleted and
rewritten in ixgbe_handle_msf() task without holding adapter->core_mtx lock.
This change is needed to maintain data coherency when sharing adapter info via
ioctl() calls.

Since handlers for abovementioned tasks will no longer act as task handlers,
but as regular functions, 'pending' parameter is removed from them.

This patch also removes ixgbe_update_link_status() call from
ixgbe_handle_link() handler. From now on, link status will be updated by
calling ixgbe_update_link_status() periodically from ixgbe_local_timer(). This
fixes problem with link flapping during changing interface state to UP.

Parameter keep_traffic is added to ixgbe_disable_intr(). This enables
ixgbe_handle_admin_task() to not disable and queue interrupts. Accordingly,
skip_traffic parameter is added to ixgbe_enable_intr() to let
ixgbe_handle_admin_task() skip enabling queues while enabling interrupts.

This patch is a port of r343621. r343621 can't be merged from current since
stable/11 contains ixgbe driver without iflib support.

Patch co-authored by Krzysztof Galazka <krzysztof.galazka@intel.com>.

Submitted by: Piotr Pietruszewski <piotr.pietruszewski@intel.com>
Reviewed by: #IntelNetworking
Sponsored by: Intel Corporation
Differential Revision: https://reviews.freebsd.org/D19711