P2P: Disable 5GHz channels in 2.4 GHz only mode

When P2P device is configured in 2.4GHz only mode supplicant
should not advertize 5GHz channels in its go negotiation frames.
  Hence disable 5GHz band channels when 2.4 GHz band only mode
selected in Wi-Fi advanced settings.

Change-Id: Ice8c9de34b19587c7e8432842a79551cc0e2333a
CRs-Fixed: 682823
Wi-Fi: Set BTCOEXMODE_DISABLED irrespective of BT's connection state

BTCOEXMODE_DISABLE has to be triggered during the DHCP phase even
on an active BT connection to ensure that Wi-Fi is given
preference over the BT.
This commit ensures the same
CRs-Fixed: 695307

Change-Id: I1eb979f03696831cb8f9e3a14b8a62f724347b64