tg3: driver sleeps indefinitely when EEH errors exceed eeh_max_freezes

The driver function tg3_io_error_detected() calls napi_disable twice,
without an intervening napi_enable, when the number of EEH errors exceeds
eeh_max_freezes, resulting in an indefinite sleep while holding rtnl_lock.

Add check for pcierr_recovery which skips code already executed for the
"Frozen" state.

Signed-off-by: David Christensen <drc@linux.vnet.ibm.com>
Reviewed-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>