netlink: completely new nlmsg hierarchy

* incapsulating all message encoding/decoding logic within nlmsg classes
* require minimal coding from rtmsg modules authors
* finally, get rid of ctypes logic
tests: move tests to another directory
generic: new NLA scalars

 * none
 * uint8
 * uint32
 * asciiz
generic: treat a message as nlmsg by default
generic: separate NLA class
generic: handle offsets and lengths properly
generic: fix_message() hack
iproute: do not ignore 0 queue
iproute: start/stop monitor mode
rtmgs: new style msg structure descriptions
netlink: pep8 issues