[Network Connection] Start dialog as affinity activity

Use affinity to keep a clear back stack to prevent caller activity from
stopped stage. If there is only NetworkRequestDialog activity in back stack,
caller will not be covered and then only become paused stage.

Bug: 128995251
Test: manual
Change-Id: I552b942810c919a41a690beff523a01aba1e4d0b
1 file changed