Remove install of obsolete ipaddr (#516)

* Support negative-valued action parameters
by converting them in the Python helper code into a positive value
whose bit pattern is the 2's complement representation of the negative
value.

* Python ipaddr package is superseded by ipaddress

vm-ubuntu-20.04/root-release-bootstrap.sh

@@ -42,4 +42,4 @@ apt-get install -qq -y --no-install-recommends --fix-missing\
   p4lang-bmv2 \
   p4lang-pi
 
-sudo pip3 install -U scapy ipaddr ptf psutil grpcio
+sudo pip3 install -U scapy ptf psutil grpcio