Typed GenericTLVs
The attached patch supports typed GenericTLV attributes, useful when
there are lots of attributes or nested data. 

Usage:

VendorSpecific {
    VendorIdentifier 0x123456;
    GenericTLV TlvCode 1 {
        GenericTLV TlvCode 2 TlvType IPAddress TlvValue 1.2.3.4;
        GenericTLV TlvCode 3 TlvType Short TlvValue 1;
        GenericTLV TlvCode 4 TlvType Char TlvValue 2;
        GenericTLV TlvCode 5 TlvType Short TlvValue 50;
    }
}