snmpagentaddress doesn't support the uppercase letters for ipv6 address

[yanjundeng]

Description

The cli "config snmpagentaddress" doesn't support the uppercase letters for ipv6 address.
In sonic /config/main.py, we should add lower() in the folllowing func for ip comparison:
def add_snmp_agent_address(ctx, agentip, port, vrf):
if agentip.lower() == ipaddr['addr'].lower():

Steps to reproduce the issue:
config snmpagentaddress add FC00:2::32 -v mgmt
IP addfress is not available
config snmpagentaddress add fc00:2::32 -v mgmt

cisco@mathilda-01:~$ show management_interface addres
Management IP address = 192.168.122.202/24
Management Network Default Gateway = 192.168.122.1
Management IP address = FC00:2::32/64
Management Network Default Gateway = fc00:2::1

Describe the results you received:

Describe the results you expected:

[wangxin]

This should be an issue of this repo: https://github.com/Azure/sonic-utilities

[xwjiang-ms]

Fixed in sonic-net/sonic-utilities#1989