networkd: dhcp server Support Vendor specific 43
Implementes https://tools.ietf.org/html/rfc2132
```
[DHCPServer]
SendRawOption=26:uint32:1400
SendRawOption=23:uint8:10
```
Frame 448: 350 bytes on wire (2800 bits), 350 bytes captured (2800 bits) on interface 0
Linux cooked capture
Internet Protocol Version 4, Src: 192.168.5.1, Dst: 192.168.5.11
User Datagram Protocol, Src Port: 67, Dst Port: 68
Dynamic Host Configuration Protocol (ACK)
Message type: Boot Reply (2)
Hardware type: Ethernet (0x01)
Hardware address length: 6
Hops: 0
Transaction ID: 0x71f8de9d
Seconds elapsed: 0
Bootp flags: 0x0000 (Unicast)
Client IP address: 0.0.0.0
Your (client) IP address: 192.168.5.11
Next server IP address: 0.0.0.0
Relay agent IP address: 0.0.0.0
Client MAC address: 1e:04:f8:b8:2f:d4 (1e:04:f8:b8:2f:d4)
Client hardware address padding:
00000000000000000000
Server host name not given
Boot file name not given
Magic cookie: DHCP
Option: (53) DHCP Message Type (ACK)
Length: 1
DHCP: ACK (5)
Option: (51) IP Address Lease Time
Length: 4
IP Address Lease Time: (3600s) 1 hour
Option: (1) Subnet Mask (255.255.255.0)
Length: 4
Subnet Mask: 255.255.255.0
Option: (3) Router
Length: 4
Router: 192.168.5.1
Option: (6) Domain Name Server
Length: 4
Domain Name Server: 192.168.5.1
Option: (42) Network Time Protocol Servers
Length: 4
Network Time Protocol Server: 192.168.5.1
Option: (101) TCode
Length: 13
TZ TCode: Europe/Berlin
Option: (43) Vendor-Specific Information
Length: 9
Value:
1701311a0431343030
Option: (54) DHCP Server Identifier (192.168.5.1)
Length: 4
DHCP Server Identifier: 192.168.5.1
Option: (255) End
Option End: 255
```