cfg80211: Add option to specify previous BSSID for Connect command

This extends NL80211_CMD_CONNECT to allow the NL80211_ATTR_PREV_BSSID
attribute to be used similarly to way this was already allowed with
NL80211_CMD_ASSOCIATE. This allows user space to request reassociation
(instead of association) when already connected to an AP. This provides
an option to reassociate within an ESS without having to disconnect and
associate with the AP.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>