Revert r330897:

This was intended to be a non-functional change. It wasn't. The commit
message was thus wrong. In addition it broke arm, and merged crypto
related code.

Revert with prejudice.

This revert skips files touched in r316370 since that commit was since
MFCed. This revert also skips files that require $FreeBSD$ property
changes.

Thank you to those who helped me get out of this mess including but not
limited to gonzo, kevans, rgrimes.

Requested by: gjb (re)

Partial merge of the SPDX changes

These changes are incomplete but are making it difficult
to determine what other changes can/should be merged.

No objections from: pfg

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

Mechanically convert to if_inc_counter().

Use define from if_var.h to access a field inside struct if_data,
that resides in struct ifnet.

Sponsored by: Nginx, Inc.

More BUS_PROBE_NOWILDCARD sweeping. Some devices here (if_ath_ahb and siba)
resist easy conversion since they implement a great deal of their attach
logic inside probe(). Some of this could be fixed by moving it to attach(),
but some requires something more subtle than BUS_PROBE_NOWILDCARD.

Mechanically substitute flags from historic mbuf allocator with
malloc(9) flags in sys/dev.

Add a trivial driver for the GXemul Ethernet device. Probably quite buggy and
certainly non-optimal, but enough for basic networking use.

Requested by: rwatson