tg3: Fix firmware event timeouts

The git commit 7c5026aa

 ("tg3: Add
link state reporting to UMP firmware") introduced code that waits for
previous firmware events to be serviced before attempting to submit a
new event.  Unfortunately that patch contained a bug that cause the
driver to wait 2.5 seconds, rather than 2.5 milliseconds as intended.
This patch fixes that bug.

This bug revealed that not all firmware versions service driver events
though.  Since we do not know which versions of the firmware do and don't
service these events, the driver needs some way to minimize the effects
of the delay.  This patch solves the problem by recording a jiffies
timestamp when it submits an event to the hardware.  If the jiffies
counter shows that 2.5 milliseconds have already passed, a wait is not
needed and the driver can proceed to submit a new event.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>