Building e.g. gnrc_border_router example on FreeBSD fails due to
missing defines related to sockets. This adds the missing header
<sys/socket.h> to fix compiling.
Some modules used a 'NATIVEINCLUDES' with different include path and no other
included directories.
It was defining basic 'include' in a different order and not using other things
defined in INCLUDES.
After doing some checks with the given include path and possible conflicting
files, there should be no conflict when using the default one.
* No common headers between all the NATIVEINCLUDES directories
* No common headers files between board/native/include, cpu/native/include and
other files in the repository (except other boards/cpus of course).
