(split) MFprojects/camlock r254895:
Add unmapped BIO support to GEOM ZERO if kern.geom.zero.clear is cleared.
(split) Create a new function to complete 802.11 mbuf transmission.

The aim of this function is to eventually be the completion entry point
for all 802.11 encapsulated mbufs.  All the wifi drivers end up doing
what is in this function so it's an easy win to turn it into a net80211
method and abstract out this code.

Ideally the drivers will all eventually be modified to queue up completed
mbufs and call this function with all the driver locks not held.
This will allow for some much more interesting software queue handling
in the future (like net80211 based A-MSDU, fast-frames, A-MPDU aggregation
and retransmission.)

Tested:

* ath(4), iwn(4)
(split) Fix the "am I a net80211 vap" check for bpf listeners.

I changed it to use if_transmit a while ago but apparently with monitor
mode the if_transmit method is overridden.

This is (mostly) a workaround until a more permanent solution can be
found.

Submitted by:	Patrick Kelsey <kelsey@ieee.org>
Approved by:	re@ (gjb)
(split) Merge branch 'CURRENT' (commit '6ef318c8')

Conflicts:
	sys/net80211/ieee80211_freebsd.c