[NET]: Remove link_watch delay for up even when we're down

Currently all link carrier events are delayed by up to a second
before they're processed to prevent link storms.  This causes
unnecessary packet loss during that interval.

In fact, we can achieve the same effect in preventing storms by
only delaying down events and unnecssary up events.  The latter
is defined as up events when we're already up.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>