sfxge(4): restore clearing of MCDI new epoch flag in common code

Submitted by:   Andy Moreton <amoreton at solarflare.com>
Sponsored by:   Solarflare Communications, Inc.
MFC after:      1 week
Differential Revision:  https://reviews.freebsd.org/D6390

sys/dev/sfxge/common/efx_mcdi.c

@@ -535,6 +535,9 @@ efx_mcdi_request_poll(
 	/* Request complete */
 	emip->emi_pending_req = NULL;
 
+	/* Ensure stale MCDI requests fail after an MC reboot. */
+	emip->emi_new_epoch = B_FALSE;
+
 	EFSYS_UNLOCK(enp->en_eslp, state);
 
 	if ((rc = emrp->emr_rc) != 0)