nwfilter: Partly initialize driver even for non-privileged users
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1211436
    
    This reverts commit b7829f959b33c6e32422222a9ed745c0da7dc696.
    
    The previous fix was not correct. Like everywhere else, a driver is a
    global variable allocated in stateInitialize function (or something
    similar for stateless drivers). Later, when a driver API is called,
    it's possible that the global variable is accessed and dereferenced.
    Now, some drivers require root privileges because they undertake some
    actions reserved only for the system admin (e.g. manipulating host
    firewall). And here's the trouble, the NWFilter state initializer
    exited too early when finding out it's running unprivileged, leaving
    the global NWFilter driver variable uninitialized. Any subsequent
    API call that tried to lock the driver resulted in dereferencing the
    driver and thus crash.
    
    On the other hand, in order to not resurrect the bug the original
    commit was fixing, Let's forbid the nwfilter define in session mode.
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
    
    Conflicts:
    	src/nwfilter/nwfilter_driver.c: Context. Code changed a bit
            since 2013.