[master] function fr_dhcpv4_encode is badly broken

[Chaigneau, Nicolas]

Likely since this commit:
https://github.com/FreeRADIUS/freeradius-server/commit/3f3afcee211407fb293186416241a149136a7464


For example, using dhcpclient:
echo "DHCP-Client-Hardware-Address=44:48:42:66:00:5a, DHCP-Transaction-Id=42, DHCP-Gateway-IP-Address=10.11.19.3, Packet-Src-Port=67, Packet-Src-IP-Address=10.11.19.3" | dhcpclient 10.11.19.28 discover


Result before (it's working, although the trace looks a bit odd: some things are displayed twice...):

Sending DHCP-Discover Id 0000002a from 10.11.19.3:67 to 10.11.19.28:67 length 300
        DHCP-Client-Hardware-Address = 44:48:42:66:00:5a
        DHCP-Transaction-Id = 42
        DHCP-Gateway-IP-Address = 10.11.19.3
        Packet-Src-Port = 67
        Packet-Src-IP-Address = 10.11.19.3
        DHCP-Opcode = Client-Message
        DHCP-Hardware-Type = Ethernet
        DHCP-Hardware-Address-Length = 6
        DHCP-Hop-Count = 0
        DHCP-Transaction-Id = 42
        DHCP-Number-of-Seconds = 0
        DHCP-Flags = 0
        DHCP-Client-IP-Address = 0.0.0.0
        DHCP-Your-IP-Address = 0.0.0.0
        DHCP-Server-IP-Address = 0.0.0.0
        DHCP-Gateway-IP-Address = 10.11.19.3
        DHCP-Client-Hardware-Address = 44:48:42:66:00:5a
        DHCP-Message-Type = DHCP-Discover
        DHCP-Network-Subnet = 10.11.19.3/32
Received DHCP-Offer Id 0000002a from 10.11.19.28:67 to 10.11.19.3:67 via eth1 length 306
(...)


Now (KO):
Some fields are wrong, for example: the first "DHCP-Gateway-IP-Address" is the value provided, but the second is reversed.
There is a "DHCP-Server-Host-Name", "DHCP-Message-Type" is missing, etc.

Sending DHCP-Discover Id 0000002a from 10.11.19.3:67 to 10.11.19.28:67 length 300
        DHCP-Client-Hardware-Address = 44:48:42:66:00:5a
        DHCP-Transaction-Id = 42
        DHCP-Gateway-IP-Address = 10.11.19.3
        Packet-Src-Port = 67
        Packet-Src-IP-Address = 10.11.19.3
        DHCP-Opcode = Client-Message
        DHCP-Hardware-Type = 0
        DHCP-Hardware-Address-Length = 0
        DHCP-Hop-Count = 0
        DHCP-Transaction-Id = 42
        DHCP-Number-of-Seconds = 0
        DHCP-Flags = 0
        DHCP-Client-IP-Address = 0.0.0.0
        DHCP-Your-IP-Address = 0.0.0.0
        DHCP-Server-IP-Address = 0.0.0.0
        DHCP-Gateway-IP-Address = 3.19.11.10
        DHCP-Server-Host-Name = "\001\006DHBf"
        DHCP-Network-Subnet = 3.19.11.10/32



Regards,
Nicolas.

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