T733: snmp.py: switch to new IP address validators
T733: snmp.py: switch to new IP address validators

Commit a30dac7c2 ("vyos package: add IP address validators") added system
wide Python validators for IP addresses. Remove duplicated code and switch
to single source.

vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x