Network Link Monitor: Add SNMPv3 Support

[gdyr]

1. Add a plugin property to select SNMP version
2. Add a plugin property (if SNMPv3 is selected) for auth type, privacy type, and auth protocol.
3. Add controls for username, password and privacy password (hidden if SNMPv2).
4. Hide the community control (if present) if using SNMPv3
5. Implement SNMPv3 methods.