Define QCA vendor roam control RSSI attributes

Define QCA vendor roam control RSSI attributes

Add three vendor roam control attributes to configure the roaming
parameters dynamically.
QCA_ATTR_ROAM_CONTROL_CONNECTED_LOW_RSSI_THRESHOLD controls the
connected AP's low RSSI threshold to trigger the neighbor lookup.
QCA_ATTR_ROAM_CONTROL_CANDIDATE_ROAM_RSSI_DIFF and
QCA_ATTR_ROAM_CONTROL_6GHZ_CANDIDATE_ROAM_RSSI_DIFF control the RSSI
difference threshold between the connected AP and the new candidate AP
for the roam to trigger.

Co-authored-by: Sunil Dutt <quic_usdutt@quicinc.com>
Signed-off-by: Sunil Dutt <quic_usdutt@quicinc.com>