BandwidthController: cleanup ipv4/v6, set/remove multiple quotas.

BandwidthController: cleanup ipv4/v6, set/remove multiple quotas.

Regroup the ipv4/ipv6 choice deeper down to avoid copypasted code.
Shared quota accross ifaces.
Single quota per ifaces.

Nothing preventing an iface from have a single and shared quota.
Might be close to having a working combination.

Added commands:
 - shared quota
  ndc bandwidth setquotas <quotaBytes> <iface> ...
  ndc bandwidth setquota <iface> <quotaBytes>
  ndc bandwidth removequota <iface>
  ndc bandwidth removequotas <iface> ...

 - quota per iface
  ndc bandwidth setiquota <iface> <quotaBytes>
  ndc bandwidth removeiquota <iface>

Change-Id: I370d223da3c8b6e16e8d0a455309ae9e0756a721