Use DHCP for eth1 and enforce MTU

If there are 2 network interfaces, acquire DHCP leases from
both. Also fix the DHCP client script to accept the MTU from
Neutron.

Change-Id: I664be34659bc41f38c69d4b3e08120488cb07f83

common-files/etc/network/interfaces

@@ -8,3 +8,10 @@ iface eth0 inet dhcp
 iface eth0 inet6 manual
     up dhcpcd -b -6 eth0
     down kill `cat /var/run/dhcpcd-eth0-6.pid` 2>/dev/null
+
+auto eth1
+iface eth1 inet dhcp
+
+iface eth1 inet6 manual
+    up dhcpcd -b -6 eth1
+    down kill `cat /var/run/dhcpcd-eth1-6.pid` 2>/dev/null

patches/series

@@ -3,3 +3,4 @@ samba4-fixes.patch
 bootloader-alignment-fix.patch
 dropbear-default-path.patch
 skeleton-profile-ps1.patch
+udhcpc-script-mtu.patch

patches/udhcpc-script-mtu.patch

@@ -0,0 +1,21 @@
+Index: buildroot/package/busybox/udhcpc.script
+===================================================================
+--- buildroot.orig/package/busybox/udhcpc.script	2017-10-14 14:55:16.374784277 -0400
++++ buildroot/package/busybox/udhcpc.script	2017-10-14 14:55:32.934958126 -0400
+@@ -8,6 +8,7 @@
+ [ -e $RESOLV_CONF ] || touch $RESOLV_CONF
+ [ -n "$broadcast" ] && BROADCAST="broadcast $broadcast"
+ [ -n "$subnet" ] && NETMASK="netmask $subnet"
++[ -n "$mtu" ] && MTU="mtu $mtu" || MTU="mtu 1500"
+ 
+ case "$1" in
+ 	deconfig)
+@@ -36,7 +37,7 @@
+ 		if [ -x /usr/sbin/avahi-autoipd ]; then
+ 			/usr/sbin/avahi-autoipd -k $interface
+ 		fi
+-		/sbin/ifconfig $interface $ip $BROADCAST $NETMASK
++		/sbin/ifconfig $interface $ip $BROADCAST $NETMASK $MTU
+ 
+ 		if [ -n "$router" ] ; then
+ 			echo "deleting routers"