MFC r360398: iflib: Stop interface before (un)registering VLAN

This is now misleadingly named for stable/11; this was meant to fix an
issue in an out-of-tree iavf(4) driver that uses iflib.

This commit actually introduces a new driver-dependent function that
iflib-using drivers can implement in order to tell iflib whether an
interface restart is needed for certain events. For this commit, this
function is only used for VLAN register/unregister events.

Sponsored by: Intel Corporation

Merge iflib changes to 11-STABLE

MFC r300147, r300153, r300154, r300215, r301563, r301567,
r302372, r307560, r307562, r307563, r307568, r308792, r311039,
r311837, r312755, r312903, r312905, r312924, r313248, r315217,
r315245, r315288, r316278, r316281, r316502, r316596, r317756,
r319917, r319921, r319984, r319989, r320059, r320609, r320611,
r321253, r321629, r321630, r322337, r322338, r322823, r323077,
r323825, r323876, r323879, r323887, r323941, r323942, r323943,
r323944, r323954, r324038, r324318, r324937, r325166, r325167,
r325168, r325201, r325241, r325245, r325487, r325494, r325901,
r326033, r326369, r326370, r326432, r326577, r326578, r326702,
r326706, r326775, r327013, r327017, r327052, r327072, r327098,
r327242, r327244, r327247, r329651, r329742, r330289, r330715,
r330721, r332419, r332422, r332729

Reviewed by: sbruno
Approved by: re (delphij@)
Sponsored by: Limelight Networks
Differential Revision: https://reviews.freebsd.org/D15142

MFC r304021: Update iflib to support more NIC designs

- Move group task queue into kern/subr_gtaskqueue.c
- Change intr_enable to return an int so it can be detected if it's not
implemented
- Allow different TX/RX queues per set to be different sizes
- Don't split up TX mbufs before transmit
- Allow a completion queue for TX as well as RX
- Pass the RX budget to isc_rxd_available() to allow an earlier return
and avoid multiple calls

Approved by: sbruno

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Import the 'iflib' API library for network drivers. From the author:

"iflib is a library to eliminate the need for frequently duplicated device
independent logic propagated (poorly) across many network drivers."

Participation is purely optional. The IFLIB kernel config option is
provided for drivers that want to transition between legacy and iflib
modes of operation. ixl and ixgbe driver conversions will be committed
shortly. We hope to see participation from the Broadcom and maybe
Chelsio drivers in the near future.

Submitted by: mmacy@nextbsd.org
Reviewed by: gallatin
Differential Revision: D5211