Update ifaces when global restriction changes.

Global restriction of background data only applies to metered
interfaces, but battery saver applies to all interfaces.  In the
very specific case where global background had been turned on while
battery saver was enabled, we'd end up with a stale battery saver
rule floating around.

This change triggers an update of iface rules when the global
restriction changes, giving us consistent behavior.

Bug: 23098198
Change-Id: I454dc71cf11d50a2e9e6122e8a801ff17039b43a