Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

MFC r257334, r257336, r257337, r257338, r257341, r257342, r257343, r257370,
r257368, r257416

Hints-only devices should return BUS_PROBE_NOWILDCARD from their probe
methods.

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

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