[intel] Work around broken reset mechanism in i219 devices

The i219 appears to have a seriously broken reset mechanism.  After
any transmit or receive activity, resetting the card will break both
the transmit and receive datapaths until the next PCI bus reset.

The Linux and BSD drivers include a convoluted workaround authored by
Intel which involves setting a bit in the undocumented FEXTNVM11
register, then transmitting a dummy 512-byte packet containing garbage
data, then reconfiguring the receive descriptor prefetch thresholds
and temporarily reenabling the receive datapath.  The comments in the
Intel fix do not even remotely match what the code actually does, and
the code accidentally leaves the transmitter enabled after use.

Experimentation suggests that an equivalent fix is to simply set the
undocumented bit in FEXTNVM11 before enabling the transmit or receive
descriptor rings.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/intel.h

@@ -195,6 +195,10 @@ struct intel_descriptor {
 #define INTEL_RAH0 0x05404UL
 #define INTEL_RAH0_AV		0x80000000UL	/**< Address valid */
 
+/** Future Extended NVM register 11 */
+#define INTEL_FEXTNVM11 0x05bbcUL
+#define INTEL_FEXTNVM11_WTF	0x00002000UL	/**< Don't ask */
+
 /** Receive address */
 union intel_receive_address {
 	struct {
@@ -308,8 +312,13 @@ enum intel_flags {
 	INTEL_NO_PHY_RST = 0x0004,
 	/** ASDE is broken */
 	INTEL_NO_ASDE = 0x0008,
+	/** Reset may cause a complete device hang */
+	INTEL_RST_HANG = 0x0010,
 };
 
+/** The i219 has a seriously broken reset mechanism */
+#define INTEL_I219 ( INTEL_NO_PHY_RST | INTEL_RST_HANG )
+
 /**
  * Dump diagnostic information
  *