board/common: ensure virtio ports have an initial speed/duplex

The speed/duplex of a virtio interface is not eenforced in any way.  The
driver initializes them to unknown/unkown:

https://github.com/torvalds/linux/blob/dccbe2047a5b0859de24bf463dae9eeea8e01c1e/drivers/net/virtio_net.c#L5375-L5381

It is however possible to set them since there are kernel subsystems
that rely on them, e.g., miimon in the bond driver, which in turn is
required for use with the 802.3ad (lacp) mode.

If we do not initialize speed/duplex the miimon will complain in the log
on virtual test systems every second:

Dec 13 22:34:08 laggy kernel: lag0: (slave e1): failed to get link speed/duplex

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

board/common/rootfs/usr/libexec/infix/init.d/25-qemu

@@ -0,0 +1,8 @@
+#!/bin/sh
+# Initialize speed/duplex of virtio interfaces
+# For virtual test systems (lacp tests)
+
+ifaces=$(ip -d -json link show | jq -r '.[] | select(.parentbus == "virtio") | .ifname')
+for iface in $ifaces; do
+    ethtool -s "$iface" speed 1000 duplex full
+done