wfd: release wifi p2p resource on disconnecting from WFD service.

Once WFD is enabled, it will keep wifi p2p resource even if WFD service
is disabled. In new interface priority scheme, this will block any
3rd-app NAN request because WFD is a system service.

Bug: 184504089
Test: execute "adb shell setprop persist.debug.wfd.enable 1"
      check p2p resource is released after calling disconnect()
Change-Id: Ic1057667e7e4bfbb2b7c44d8949043e62d145356