Fix a never-ending loop with multiple radios in wpa_supplicant

Fix a never-ending loop with multiple radios in wpa_supplicant

Commit 202dec2a94695a696236ee5a2ad1be0905ccea14 introduced a never
ending loop for a case where a single wpa_supplicant process is used
with multiple radios. Fix this by advancing the iface pointer properly
to the next interface in the loop until a NULL pointer is hit.

Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>