Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

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

MFH: sync the netmap code with the one in HEAD
(enhanced VALE switch, netmap pipes, emulated netmap mode).
See details in the log for svn 261909.

Merge from head: sync the netmap code with the one in HEAD

MFC: sync the version of netmap with the one in HEAD, including device
drivers (mostly simplifying the code in the interrupt handlers).

On passing, also merge r250414, which is related to netmap
and the use of lem/em in virtual machines.

MFH: sync netmap with the version in HEAD

MFC r241643: Avoid panic when a netmap instance cannot obtain memory.

A uint32_t is always >= 0.

Sponsored by: ADARA Networks

forgot two files in the previous commit...