tg3: Clear RECOVERY_PENDING with reset_task_cancel

If an error happens in the tx completion thread, tg3_reset_task will be
scheduled and TX_RECOVERY_PENDING will be set.  The TX_RECOVERY_PENDING
flag causes tg3_poll[_msix] to return early before doing much of its
work.  Tg3_reset_task() gets canceled when the configuration of the
device is changing, which always results in a chip reset.  When this
happens, the TX_RECOVERY_PENDING flag may be left set, which would
unnecessarily hinder tg3_poll from doing work.  This patch fixes the
problem.

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