net: if: Make sure only allowed threads can access syscalls

Make sure that only those threads that have been granted access
to net_if objects, can call the functions that modify net_if data.

The CONFIG_NET_IF_USERSPACE_ACCESS config option is also removed
as it is no longer needed after this change.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
4 files changed