Changes

pcap-client: Allow recording on several interfaces

This commit enables basic support for multi-interface capturing.
The transmitted data to the osmo-pcap-server is not yet in pcapng
format, which means no information regarding the iface it was captured
on is provided when opening the resulting pcap file.

Related: SYS#5822
Change-Id: I082b0bd38cf1829937c5e643f0ee31f9d56a07a7