bnx2x: Prevent mistaken hangup between driver & FW

When system CPU is stressed it's possible that the driver will not be able
to pulse the FW every second, which will cause the log to be filled with
error messages.

Increasing the threshold to 5 seconds seems to be enough to eliminate the
issue.

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