Rather than defining the same values in two places and having to do
conflict resulution on the name in LKPI, change the defines to an
enum in net80211.  In addition to de-duplication this also gives us
value checks in certain cases.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Reviewed by:	adrian
Differential Revision: https://reviews.freebsd.org/D36250

Replace a malloc() by IEEE80211_MALLOC().
For malloc flags even in the local ieee80211_freebsd.c there was a mix
of both versions M_ and IEEE80211_M_.
Consistently use the IEEE80211_M_ malloc options everywhere.
If the field is changed for malloc, it'll also be changed for the
other accessor functions taking a "how" field to avoid any confusion.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Reviewed by:	adrian
Differential Revision: https://reviews.freebsd.org/D36249

Make sure the given IE length fits into the total length left when
parsing through the information elements.  In theory I would say
discard everything if there is an error but that proves hard with
the current code.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Reviewed by:	adrian
Differential Revision: https://reviews.freebsd.org/D36245

Implement some basic kfifo pieces as needed by drivers.

MFC after:	2 weeks
Reviewed by:	wulf, hselasky
Differential Revision: https://reviews.freebsd.org/D35829

The IFF_DRV_RUNNING flag is used to see if the interface needs
to be temporarily brought down during MTU change sequence.
The problem here is that this flag is cleared in mvneta_stop_locked,
resulting in the reinitialization logic never being executed after
MTU has been changed.
Fix that by saving the flag value before the interface is brought down.

Reported by:	Jérôme Tomczyk <jerome.tomczyk@stormshield.eu>
Approved by:	mw(mentor)
Obtained from:	Semihalf
Sponsored by:	Stormshield
MFC after:	2 weeks