The protocol for the control interface is wrapped inside the ip.access header
with the IPAC_PROTO_OSMO protocol ID (0xee). Inside the ip.access header is
a struct ipaccess_head_ext with protocol ID 0x00 which indicates the control
interface.

After that the actual protocol is text based:

* Getting the value of a variable
-> GET <id> <var>
<- GET_REPLY <id> <var> <val>
or ERROR <id> <reason>

* Setting the value of a variable
-> SET <id> <var> <val>
<- SET_REPLY <id> <var> <val>
or ERROR <id> <reason>

* A value changes which triggers a trap
<- TRAP <var> <val>

<id> needs to be unique within a connection. '0' is not allowed