pcap: ERF per-Host ID/Source ID interface support

pcap: ERF per-Host ID/Source ID interface support

Add encap_priv pointer to libpcap_t.
Initialize erf_priv when ENCAP_ERF.
Use erf_populate_interface_from_header() to dynamically create interfaces.
Free encap_priv on pcap_close.

Ping-Bug: 12303
Change-Id: Ieda425ef3e50a124d9c38ee4538aa3644128ce60
Reviewed-on: https://code.wireshark.org/review/15362
Petri-Dish: Alexis La Goutte <alexis.lagoutte@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>