cfg80211: Allow non-zero indexes for device specific pair-wise ciphers

Some vendor specific cipher suites require non-zero key indexes for pairwise
keys, but as of currently, the cfg80211 does not allow it.

As validating they cipher parameters for vendor specific cipher suites is the
job of the driver or hardware/firmware, change the cfg80211 to allow also
non-zero pairwise key indexes for vendor specific ciphers.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>