[BRIDGE]: handle speed detection after carrier changes

Speed of a interface may not be available until carrier
is detected in the case of autonegotiation. To get the correct value
we need to recheck speed after carrier event.  But the check needs to
be done in a context that is similar to normal ethtool interface (can sleep).

Also, delay check for 1ms to try avoid any carrier bounce transitions.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>