MFC r249952:

  Fix examples for overriding INSTALL to not suggest hardcoding
  'install' since it breaks buildworld after the introduction and
  use of 'install -l' in r245752. Overriding INSTALL causes
  /usr/bin/install to be used instead of the proper
  /usr/src/tools/install.sh which handles the new flag.
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.