qemu: misc fixes for new qemu release

- Ensure qemu is built in same ubuntu distro as where it is run
- Add new libslirp-dev dep to docker container that executes qemu

Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
Change-Id: Iaa58d097de0377e4bb5ee229c5ec267ebe4565a7
diff --git a/qemu-build.sh b/qemu-build.sh
index 624f068..c17b654 100755
--- a/qemu-build.sh
+++ b/qemu-build.sh
@@ -108,7 +108,7 @@
 # !!!
 
 Dockerfile=$(cat << EOF
-FROM ${DOCKER_BASE}ubuntu:latest
+FROM ${DOCKER_BASE}ubuntu:jammy
 
 ${PROXY}