[dev][virtio][net] add working implementation of a virtio network interface

-Not optimized yet, but should be pretty complete. Tested against qemu.
-Add switches to qemu script to allow running with a tap interface.
-Enable minip by default on vexpress-a9 platform

scripts/do-qemuarm

@@ -4,18 +4,23 @@ function HELP {
     echo "help:"
     echo "-b a virtio block device"
     echo "-n a virtio network device"
+    echo "-t a virtio tap network device"
     echo "-h for help"
     echo "all arguments after -- are passed to qemu directly"
     exit 1
 }
 
 DO_NET=0
+DO_NET_TAP=0
 DO_BLOCK=0
+SUDO=""
 
-while getopts bhn FLAG; do
+while getopts bhnt FLAG; do
     case $FLAG in
         b) DO_BLOCK=1;;
         n) DO_NET=1;;
+        t) DO_NET_TAP=1
+           SUDO="sudo ";;
         h) HELP;;
         \?)
             echo unrecognized option
@@ -28,6 +33,7 @@ shift $((OPTIND-1))
 ARGS=" -machine vexpress-a9 -m 512 -kernel build-vexpress-a9-test/lk.elf -nographic"
 BLOCK_ARGS=" -drive if=none,file=blk.bin,id=blk,format=raw -device virtio-blk-device,drive=blk"
 NET_ARGS=" -netdev user,id=vmnic,hostname=qemu -device virtio-net-device,netdev=vmnic"
+NET_TAP_ARGS=" -netdev tap,id=vmnic -device virtio-net-device,netdev=vmnic"
 
 echo DO_BLOCK = $DO_BLOCK
 echo DO_NET = $DO_NET
@@ -38,7 +44,10 @@ fi
 if [ $DO_NET == 1 ]; then
     ARGS+=$NET_ARGS
 fi
+if [ $DO_NET_TAP == 1 ]; then
+    ARGS+=$NET_TAP_ARGS
+fi
 
 make vexpress-a9-test -j4 &&
-echo qemu-system-arm $ARGS $@ &&
-qemu-system-arm $ARGS $@
+echo $SUDO qemu-system-arm $ARGS $@ &&
+$SUDO qemu-system-arm $ARGS $@