freenetconfd: add initial modules handling

Also simplify netconf message creation.

Signed-off-by: Petar Koretic <petar.koretic@sartura.hr>
messages: drop unused defines

Signed-off-by: Petar Koretic <petar.koretic@sartura.hr>
plugins: add initial ietf-system plugin

gcc -Wall -shared -o ietf-system.so -fPIC ietf-system.c -I../include --std=gnu11

Signed-off-by: Petar Koretic <petar.koretic@sartura.hr>
cmake: drop libssh

Signed-off-by: Petar Koretic <petar.koretic@sartura.hr>
cmake: switch to gnu11

Signed-off-by: Petar Koretic <petar.koretic@sartura.hr>
freenetconfd: fix base 1.1 message header handling

Also makes rpc debug output more consistent.

Signed-off-by: Petar Koretic <petar.koretic@sartura.hr>