net: wireless: bcmdhd: new feature for Roaming.

	1) The functionality help to prevent the device from doing roam
	scan forever in the environment which has just one AP nearbyt,
	but the RSSI of the AP is -75dbm ~ 78dbm
	2) The feature will set the roam trigger from -75dbm to -85dbm
	in case that there are only one AP.
	3) The value will be reset to -75dbm after disconnecting from
	current AP.
	4) This patch will Fixed Google issue: [10718651]
	   WiFi draining battery life even while phone connected to charge
	5) Enable flow control in DHD driver to fix
	   10430352 UDP speed is less than 40% of TCP speed with LInksys
	   WRT110
Signed-off-by: Ecco Park <eccopark@broadcom.com>