Add libpcap-dev dependency for voltha unit tests

Change-Id: Id6886c7b321a74842680d998e4b2a8f4f6c853b8
diff --git a/packer/provision/basebuild.sh b/packer/provision/basebuild.sh
index 45b0395..91a813f 100644
--- a/packer/provision/basebuild.sh
+++ b/packer/provision/basebuild.sh
@@ -56,6 +56,7 @@
         curl \
         git \
         less \
+        libpcap-dev \
         libxml2-utils \
         maven \
         nodejs \