bnx2x: Fix rare self-test failures

On rare occasions, self test link may fail since the link is
being sampled while it's still being stabilized.
To correct this behaviour, try to sample the link for 2 seconds
prior to declaring a failure.

Signed-off-by: Yaniv Rosner <yanivr@broadcom.com>
Signed-off-by: Yuval Mintz <yuvalmin@broadcom.com>
Signed-off-by: Ariel Elior <ariele@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>