Mbb success metrics: lingering duration histogram

Get metrics on the lingering duration after the primary switches to
secondary as a result of MBB. A long lingering duration means apps will
have more time to switch networks.

Updated-PDD: TRUE
Bug: 180974604
Test: atest com.android.server.wifi
Change-Id: I247875bdceffb62024abc83a30899e028dd1e328
9 files changed