bnx2x: Using singlethread work queue

Since slow-path events, including link update, are handled in
work-queue, a race condition was introduced in the self-test that
sometimes caused the link status to fail: the self-test was running
under RTNL lock, and if the link-watch was scheduled it stoped the
shared work-queue (waiting for the RTNL lock) and so the link update
event was not handled until the self-test ended (releasing the RTNL
lock) with failure (since the link status was not updated)

Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>