tg3: Fix io failures after chip reset

Commit f2096f94, entitled
"tg3: Add 5720 H2BMC support", needed to add code to preserve some bits
set by firmware.  Unfortunately the new code causes throughput to stop
after a chip reset because it enables state machines before they are
ready.  This patch undoes the problematic code.  The bits will be
restored later in the init sequence.

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