As discussed in #2725, this commit renames a number of stacksize constants to
better convey their intended usage. In addition, constants for thread priority
are given a `THREAD_` prefix. Changes are:
* KERNEL_CONF_STACKSIZE_PRINTF renamed to THREAD_EXTRA_STACKSIZE_PRINTF
* KERNEL_CONF_STACKSIZE_DEFAULT renamed to THREAD_STACKSIZE_DEFAULT
* KERNEL_CONF_STACKSIZE_IDLE renamed to THREAD_STACKSIZE_IDLE
* KERNEL_CONF_STACKSIZE_MAIN renamed to THREAD_STACKSIZE_MAIN
* Move thread stacksizes from kernel.h to thread.h, since the prefix changed
* PRIORITY_MIN renamed to THREAD_PRIORITY_MIN
* PRIORITY_IDLE renamed to THREAD_PRIORITY_IDLE
* PRIORITY_MAIN renamed to THREAD_PRIORITY_MAIN
* Move thread priorities from kernel.h to thread.h since the prefix has changed
* MINIMUM_STACK_SIZE renamed to THREAD_STACKSIZE_MINIMUM for consistency
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*.
