e1000: omit stats for broken counter in 82543

The 82543 chip does not count tx_carrier_errors properly in FD mode;
report zeros instead of garbage.

Originally from Jesse Brandeburg <jesse.brandeburg@intel.com>, rewritten
to use feature flags by me.

Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/net/e1000/e1000_hw.h

@@ -1460,6 +1460,7 @@ struct e1000_hw {
 	boolean_t		mng_reg_access_disabled;
 	boolean_t		leave_av_bit_off;
 	boolean_t		kmrn_lock_loss_workaround_disabled;
+	boolean_t		bad_tx_carr_stats_fd;
 };