MFC r260702 (by melifaro):
  Fix ipfw fwd for IPv4 traffic broken by r249894.

  Problem case:
  Original lookup returns route with GW set, so gw points to
  rte->rt_gateway.
  After that we're changing dst and performing lookup another time.
  Since fwd host is most probably directly reachable, resulting
  rte does not contain rt_gateway, so gw is not set. Finally, we
  end with packet transmitted to proper interface but wrong
  link-layer address.
MFC r261080:
The posix_fallocate(2) syscall should return error number on error,
without modifying errno.

MFC r261290:
The posix_madvise(3) and posix_fadvise(2) should return error on
failure, same as posix_fallocate(2).