[CLI] config vlan dhcp_relay is accepting ipv6 addresses and restarting the service

[vivekrnv]

Description

dhcpv6 relay needs config only in DHCP_RELAY table and not in VLAN table and thus the "config vlan" cli shouldn't accept an ipv6 address.

Steps to reproduce the issue:

1.  config vlan add 100
2.  config vlan dhcp_relay add 100 fc00::3:2

Describe the results you received:

Added DHCP relay destination addresses ['fc00::3:2'] to Vlan100
Restarting DHCP relay service...

Describe the results you expected:

CLI should reject ipv6 address with a relevant message.

Output of show version:

Seen on all labels