core/internal/network: use DHCP router/gateway

This makes us actually set up a default route now. We also stop using github.com/insomniacslk/dhcp types, and instead use our type for the DHCP status. Finally, we also comment the DHCP client a bit better.

This fixes T651.

Test Plan: lacking a regression test, working on one now.

Bug: T651

X-Origin-Diff: phab/D403
GitOrigin-RevId: caead83016cfe2f1783fad33e8d71723a3a32057
diff --git a/core/scripts/launch.sh b/core/scripts/launch.sh
index bc91f0c..3f4e9b9 100755
--- a/core/scripts/launch.sh
+++ b/core/scripts/launch.sh
@@ -13,7 +13,7 @@
     -drive if=pflash,format=raw,readonly,file=external/edk2/OVMF_CODE.fd \
     -drive if=pflash,format=raw,snapshot=on,file=external/edk2/OVMF_VARS.fd \
     -drive if=virtio,format=raw,snapshot=on,cache=unsafe,file=core/smalltown.img \
-    -netdev user,id=net0,hostfwd=tcp::7833-:7833,hostfwd=tcp::7834-:7834,hostfwd=tcp::6443-:6443,hostfwd=tcp::7835-:7835 \
+    -netdev user,id=net0,net=10.42.0.0/24,dhcpstart=10.42.0.10,hostfwd=tcp::7833-:7833,hostfwd=tcp::7834-:7834,hostfwd=tcp::6443-:6443,hostfwd=tcp::7835-:7835 \
     -device virtio-net-pci,netdev=net0 \
     -chardev socket,id=chrtpm,path=tpm-socket \
     -tpmdev emulator,id=tpm0,chardev=chrtpm \