VIRT-PHY: Use IPv4 multicast groups for private / local scope
VIRT-PHY: Use IPv4 multicast groups for private / local scope

The addresses in the original code make little sense:
* 224.0.0.1 is "All systems on this subnet" and not routed
  outside the local ethernet segment
* 225.0.0.1 is in a RESERVED range that shouldn't be used

Change-Id: Iba1ae69f3f193a33f1da343c6562f67bd8d3557f

osmocom/osmo-bts,osmocom/osmo-bts,osmocom/osmo-bts