This avoids scheduling in atomic context and also means that IRQs
will only be deferred for relatively short periods of time.

Previously discussed in:
http://article.gmane.org/gmane.linux.network/155024Reported-by: Arne Nordmark <nordmark@mech.kth.se>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>