HDMI: Keep active source on <Set Stream Path> to ancestor

If <Set Stream Path> targeting an ancestor address is received while this device is the
active source, wait to see if a new Active Source is declared, as a parent switch might
be changing paths.

E.g. TV [0.0.0.0] -- AVR [3.0.0.0] -- Playback [3.1.0.0] (Active Source)
TV sends <Set Stream Path> [3.0.0.0]

Possible outcomes:
 - AVR sends <Routing Information> [3.2.0.0] -> Playback [3.1.0.0] is no longer AS.
 - AVR sends <Routing Information> [3.1.0.0] -> Playback [3.1.0.0] stays <AS>.
 - AVR sends no relevant CEC message -> Playback [3.1.0.0] stays <AS>.

Test: atest HdmiCecLocalDevicePlayback
Flag: EXEMPT bugfix
Bug: 405800336
Bug: 406374736
Change-Id: Ic1602f525d23a8e8da5ccd05a2421e6bf96261ea