Saves two unnecessary function calls.

Removes the old interface.

There's no need to run config_load from core directly, can be done by
auto_init.

Since the 4-byte CPU ID on native is in most cases generated from the 2-byte
PID of the native process, choosing the lower half of the hash of the CPU ID to
set the radio address led to always setting it to the hash of 0 in this
cases. This changes it to use both halves of the hash and taking the
modulus so this corner cases can be avoided.

Currently, the tcp and udp implementations are bound to each other in a
module called *destiny*. Thus, when using only one of them then the
other one gets also compiled into the binary and initialized,
which results in unnecessary RAM usage and workload for the CPU.

The approach in this PR defines a common module named *socket_base*,
which contains functions used by the posix layer. Compiled by it's own,
those functions return negative error codes, to symbolize upper layers
that they are not supported. When also including the modules *udp* or
*tcp* respectively, functions from *socket_base* get overwritten with the
correct functionality.

Defining *udp* or *tcp* in a Makefile also includes *socket_base*.
Defining *pnet* in a Makefile also includes *socket_base*.

Eliminates special treatment of the hwtimer module and makes it a
mandatory part of the kernel.

Include headers only if respective module is built.
Fixes building for msb-430.
Prevents possible build breaks in the future.