cfg80211: basic support for PBSS network type

PBSS (Personal Basic Service Set) is a new BSS type for DMG
networks. It is similar to infrastructure BSS, having an AP-like
entity called PCP (PBSS Control Point), but it has few differences.
PBSS support is mandatory for 11ad devices.

Add support for PBSS by introducing a new PBSS flag attribute.
The PBSS flag is used in the START_AP command to request starting
a PCP instead of an AP, and in the CONNECT command to request
connecting to a PCP instead of an AP.

Signed-off-by: Lior David <liord@codeaurora.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>