Implement full Vendor Tlv127 support

[manojnacsl]

Implement full Vendor Tlv127 support

• Encode/decode functions for GET/PUT operations (honoring tlvid.type, tlvid.vendor, subtype, length, value) with provision for extensibility in supporting multiple subtypes for a vendor-id
• Use IANA-PEN for Vendor-ID assignments
• Enable agent-side support for Registration
• Enable agent-side support for Periodic metric refresh
• Protobuf updates conforming to spec
• FND currently does not support Vendor Tlv127 - GET/POST(config-push), registration, periodic metric refresh support needs to be implemented in FND.

TLV-ID          NAME              OPERATION
---------------------------------------------------
1. TLV127   VENDOR TLV    GET
2. TLV127   VENDOR TLV    POST