hs-test: add libunwind dependency to vpp dockerfile

- missing from https://gerrit.fd.io/r/c/vpp/+/40929 due to hst not running in CI yet.

Type: fix

Change-Id: Ib5d9b877725624ef7de9f2be5e517609aec7c5a1
Signed-off-by: Dave Wallace <dwallacelf@gmail.com>

extras/hs-test/docker/Dockerfile.vpp

@@ -5,7 +5,7 @@ FROM ubuntu:${UBUNTU_VERSION}
 RUN apt-get update \
  && apt-get install -y openssl libapr1 libnuma1 libsubunit0 \
     iproute2 libnl-3-dev libnl-route-3-dev python3 iputils-ping  \
-    vim gdb \
+    vim gdb libunwind-dev \
  && rm -rf /var/lib/apt/lists/*
 
 ENV DIR=vpp-data/lib/vpp_plugins