network: DHCPv6 - Add support to send vendor class information

network: DHCPv6 - Add support to send vendor class information

Frame 1: 177 bytes on wire (1416 bits), 177 bytes captured (1416 bits) on interface veth-peer, id 0
Ethernet II, Src: 1e:04:f8:b8:2f:d4 (1e:04:f8:b8:2f:d4), Dst: IPv6mcast_01:00:02 (33:33:00:01:00:02)
Internet Protocol Version 6, Src: fe80::1c04:f8ff:feb8:2fd4, Dst: ff02::1:2
User Datagram Protocol, Src Port: 546, Dst Port: 547
DHCPv6
    Message type: Solicit (1)
    Transaction ID: 0x5ca46b
    Rapid Commit
    Identity Association for Non-temporary Address
    Fully Qualified Domain Name
    Vendor Class
        Option: Vendor Class (16)
        Length: 23
        Value: 0000ab11000048656c6c6f3a686f773a6172653a796f75
        Enterprise ID: Tom Gundersen (systemd) (43793)
        vendor-class-data: Hello:how:are:you
    Identity Association for Prefix Delegation
    Option Request
    Client Identifier
    Elapsed time