Fix parsing of compressed IPv4 Updates

We were using the Flags field instead of the AE field when parsing
compressed IPv4 prefixes in Update messages.  This bug shouldn't
trigger, since we never use compression with IPv4.
Refactor acceptance of new local connections

The various cases of success or failure are quite intricate.  Since we
plan to intricate it further in an upcoming commit, it's better to
refactor it now.
Prevent a DoS by making the local interface non-blocking

This prevents a DoS from the local interface, which could be performed
by any user on the system running babeld.

A malicious attacker could connect to the local interface, and then
wait without reading any data.  When the send buffer eventually fills
up, babeld would block; as a result, it would become completely
inoperative.

Note that 'local_server_socket' is already non-blocking, but the
sockets spawned by accept() don't inherit this flag.  From accept(2):

  On Linux, the new socket returned by accept() does not inherit file
  status flags such as O_NONBLOCK and O_ASYNC from the listening socket.
Revert "Kernel_socket: do not use the RTF_PROTO2 flag."

This flag is easiest way to filter out babel's route in the
kernel_routes function.

This reverts commit 0845af770694f315398c992c3e9f151f37cbe43a.
BSD: do not attempt atomic route changes.

This is buggy on OS X, at least. As for linux we choose to be safe and
we deactivate atomic route changes on all BSDs.
Cap neighbour cost to INFINITY

With large txcost and rxcost, the calculated cost to a neighbour can
exceed 65535, i.e. INFINITY.  This is not a real issue, since any cost
over 65535 is equally seen as infinity.

However, it can confuse other tools (e.g. babelweb) who wouldn't
expect a cost higher than infinity.
Make babeld request sending conform to the RFC.

The prefix field’s size is Plen/8 rounded upwards.
Update CHANGES.
Update CHANGES.
Give names to the various types of sub-TLV
Fix headers for NetBSD
Update CHANGES for 1.4.3.
Update website address.
Merge remote-tracking branch 'master' into source-specific

Conflicts:
	kernel_socket.c
	message.c