The enb_proxy now captures the local address and port of the S1GW-MME SCTP connection (mme_saddr/mme_sport) at comm_up and includes them in conn_info(). Expose this info through the REST API (EnbItem schema), show it as a new column/row in the CLI (enb_list/enb_info).
The full enb_list table with all address columns is too wide to fit on a page and does not render well in PDF. Collapse the address columns with '...'; add a note that they are omitted for readability.
enb_{proxy,registry}: signal MME conn info on SCTP comm_up
Previously, mme_aid/mme_saddr/mme_sport were only signalled to the enb_registry once the S1 Setup procedure completed. This meant the REST API could not show MME connection details for eNBs stuck in wait_s1setup_rsp state (e.g. due to a slow or retrying MME).
Add notify_mme_comm_up/2, called at SCTP comm_up, which stores the full conn_info (including mme_aid, mme_saddr, mme_sport) in the registry as soon as the SCTP connection is established.
notify_mme_connected/2 is simplified to notify_mme_connected/1: it now only flips the state to 'connected', since conn_info is already stored.
enb_proxy: split conn_info() into mme_conn_info() and proxy_info()
The old conn_info() conflated two distinct concerns: the MME SCTP connection info stored in enb_registry (aid, saddr, sport) and the broader operational state used for introspection (handler pid, enb connection info, etc.). Mixing them forced enb_registry to hold a handler pid it has no business knowing about, and required rest_server to extract that pid just to reach s1ap_proxy for E-RAB listing.
Split into two distinct types:
* mme_conn_info() - pure MME SCTP connection info (aid, saddr, sport), stored in the enb_registry and signalled via notify_mme_comm_up/2. The `mme_` prefix is dropped from field names as the type name provides the context.
* proxy_info() - richer operational snapshot (handler, enb_handle, enb_conn_info, mme_conn_info, genb_id_str, mme_info), returned by fetch_info/1 for introspection/debugging purposes.
Additionally:
* Add fetch_erab_list/1 to enb_proxy, delegating internally to s1ap_proxy:fetch_erab_list/1 via the cached handler pid. This allows the rest_server to obtain a list of E-RAB without having to obtain pid of the s1ap_proxy and interact with it.
* Remove separate enb_aid/mme_aid/mme_saddr/mme_sport state fields; enb_aid is now read directly from enb_conn_info, and the MME fields are grouped in mme_conn_info.
As a bonus, `tried_mmes` now only serves its actual purpose - tracking which MMEs have already been tried for selection filtering - rather than being abused as a way to retrieve the current MME name.
rest_server: fix TOC/TOU race when listing/fetching E-RABs
The list of E-RAB FSM pids is a snapshot taken at one point in time. By the time we interrogate each erab_fsm process individually, any of them may have already terminated (e.g. bearer released mid-request). The current code fails to generate a response if this happens.
* fetch_erab_info/1: add a pid() clause that wraps erab_list_item/1 in a try/catch, returning 'error' if the process is gone.
* fetch_erab_info/1: catch both exit forms ** `{noproc, _}` raised by gen_statem:call/2 on a monitored pid, and ** the bare noproc atom for other code paths.
* fetch_erab_list/1: switch from lists:map to lists:filtermap and call fetch_erab_info/1 per E-RAB, silently dropping any that died between the snapshot and the per-process interrogation.
