Cells: Make bandwidth_update_interval configurable

Bandwidth updates have been known to cause queues to backup. This
configuration provides a way to throttle or disable bandwidth updates as
necessary.

Fixes bug 1199899

Change-Id: Ic57e6e3915a9b97155b9fd677e1b96e6aaadb17e
Merge "Cells: Make bandwidth_update_interval configurable"