Enable CastTile when connected as hotspot

If the device is acting as a wifi hotspot and it has at least 1 device
connected, enable the CastTile. Before this CL, as it's not connected to
a WiFi (external), it would be disabled with a "Wi-Fi not connected"
message.

Test: manual
Test: CastTileTest
Fixes: 168981668
Change-Id: I09175a4a8f5adfff1a4ed78b9328680365bb12f2