Added Makefiles for XIA
Added socket constants for XIA
Add Ethernet types ETH_P_XIP and ETH_P_NWP
Increase maximum socket address size

See discusion at the following link:

https://github.com/AltraMayor/XIA-for-Linux/wiki/sizeof%28struct-sockaddr_xia%29-compromise
Added CONFIG_EXPERIMENTAL dependency

Also, xia.ko can be build as a module now.
Added a hello-world version of module xia.ko
Added a skeleton for the first XIA protocol

The first XIA protocol is `XIA_RAW'.

The code doesn't do anything besides issuing messages in dmesg,
the goal is to get a `working' template in which specific features
can be worked out.

The code isn't `working' yet, it still misses pieces such as
struct proto_ops, and network namespace.
Added placeholders for XIA's network namespace

The code at least compiles.
Now one can create XIA sockets

The code barely does anything, its relevance is that
having a `working' skeleton is a better starting point.
Added essential code to receive user-land calls
Improved XIA address conversion functions

xia_ntop:
  - Edges' indexes greater than 'z' are made equal to '+'.
  - Empty edges are represented by '*'.
  - Added option include_nl to use token ":\n" instead of ":".
  - Added marker '!' when a address is invalid.

xia_pton:
  - Added option invalid_flag to inform that the '!' marker was seen.
  - Support node separator ":\n".
  - Support empty edges (i.e. '*').
  - Make sure that the whole string is parsed.
  - Require 40 hexadecimal digits for XID.
  - Accept variable number of edges.
  - Improved support for '\0'-terminated strings.

xia_test_addr:
  - Return the number of nodes in addr.
Implemented the first version of net/xia/af_xia.c

The functions in net/xia/af_xia.c heavy follow those in net/ipv4/af_inet.c
It only implements the necessary code for raw XIA sockets, other transport
protocols will require reviews of this file.
Added tests to function xia_test_addr

- Enforced topological order; it's a cheap way to test acyclicity.
- Enforced a single component.
Cosmetically improved function xia_ntop

Listing only the present edges when a address is valid;
it was marked as a ToDo in the code.
Added tags __init and __exit
Adjustments for userland applications

Function xia_pton isn't necessary in the kernel, and header net/xia.h
now can be included by applications.
Added data structures for XIA routing tables
Added support to netnamespace

For now, only fib is in struct net.
Added support to rtnetlink in XIA stack

Message types: RTM_NEWROUTE, RTM_DELROUTE, RTM_GETROUTE.
Added skeleton of AD principal module