cfg: separate PFCP Node ID from PFCP local address
The PFCP protocol features a Node ID, which can be used to uniquely identify
PFCP endpoints across different interfaces. The Node ID can be a fully-qualified
domain name (FQDN), or IP address. Currently, osmo-hnbgw has no support for
using an FQDN as Node ID, and requires the 'local-addr' to be configured, which
it uses as Node ID.
Instead, we should separate the concepts of which local interface to use from the Node ID sent in-band.
pfcp_endpoint.h already has separate fields in osmo_pfcp_endpoint_cfg for local_addr and local_node_id, but osmo-hnbgw only features a pfcp / local-addr config option.
osmo-hnbgw is the first PFCP CPF implementation. Since other CPF may be added in the future, it would make sense to implement the PFCP endpoint configuration bits into libosmo-pfcp, including a FQDN node id set separately from the local-addr, and then use that in osmo-hnbgw.
(Similar to how osmo-msc, osmo-bsc and osmo-hnbgw use mgcp_client_vty_init() from libosmo-mgcp-client.)
- implement common CPF client VTY config, #5648
- use CPF client VTY config in osmo-hnbgw
- update doc/manual/chapters/running.adoc