sky2: fix suspend/resume races

There are a couple of possible races on suspend/resume.
First the driver needs to block new packets from being queued for Tx.
The other less likely problem is the watchdog timer going off
during resume.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>