slirp: add a fake NC-SI backend

NC-SI (Network Controller Sideband Interface) enables a BMC to manage
a set of NICs on a system. This model takes the simplest approach and
reverses the NC-SI packets to pretend a NIC is present and exercise
the Linux driver.

The NCSI header file <ncsi-pkt.h> comes from mainline Linux and was
untabified.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Acked-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: Jason Wang <jasowang@redhat.com>
diff --git a/include/net/eth.h b/include/net/eth.h
index afeb45b..09054a5 100644
--- a/include/net/eth.h
+++ b/include/net/eth.h
@@ -209,6 +209,7 @@
 #define ETH_P_IPV6                (0x86dd)
 #define ETH_P_VLAN                (0x8100)
 #define ETH_P_DVLAN               (0x88a8)
+#define ETH_P_NCSI                (0x88f8)
 #define ETH_P_UNKNOWN             (0xffff)
 #define VLAN_VID_MASK             0x0fff
 #define IP_HEADER_VERSION_4       (4)