api,modem-3gpp: new 'InitialEpsBearer' property

This property contains the DBus path of a Bearer object of type
MM_BEARER_TYPE_DEFAULT_ATTACH, which is automatically exposed by the
modem when registered in the LTE network.

Unlike standard bearer objects created by the user, this bearer won't
allow any connection/disconnection request, as its status is bound to
the LTE registration exclusively.

The bearer settings exposed by the object include the APN details that
have been used during the initial packet network attach, which may be
defined by modem settings (e.g. if previously configured in the
firmware which APN to use for the given SIM card operator) or by the
network itself (e.g. if none configured, or if a network override is
required as when roaming).

The bearer object will be created as soon as the LTE attach status
details are known, and only while the modem is enabled. The
implementation allows modems to update the LTE attach status details
during runtime, so the bearer object with the settings may be
recreated during runtime as well.

docs/reference/libmm-glib/libmm-glib-sections.txt

@@ -277,8 +277,13 @@ mm_modem_3gpp_dup_operator_name
 mm_modem_3gpp_get_enabled_facility_locks
 mm_modem_3gpp_get_registration_state
 mm_modem_3gpp_get_subscription_state
-mm_modem_3gpp_get_eps_ue_mode_operation
 mm_modem_3gpp_get_pco
+mm_modem_3gpp_get_eps_ue_mode_operation
+mm_modem_3gpp_get_initial_eps_bearer_path
+mm_modem_3gpp_dup_initial_eps_bearer_path
+mm_modem_3gpp_get_initial_eps_bearer
+mm_modem_3gpp_get_initial_eps_bearer_finish
+mm_modem_3gpp_get_initial_eps_bearer_sync
 <SUBSECTION Methods>
 mm_modem_3gpp_register
 mm_modem_3gpp_register_finish
@@ -291,6 +296,7 @@ mm_modem_3gpp_set_eps_ue_mode_operation_finish
 mm_modem_3gpp_set_eps_ue_mode_operation_sync
 <SUBSECTION Standard>
 MMModem3gppClass
+MMModem3gppPrivate
 MM_IS_MODEM_3GPP
 MM_IS_MODEM_3GPP_CLASS
 MM_MODEM_3GPP
@@ -1762,6 +1768,8 @@ mm_gdbus_modem3gpp_get_subscription_state
 mm_gdbus_modem3gpp_get_eps_ue_mode_operation
 mm_gdbus_modem3gpp_get_pco
 mm_gdbus_modem3gpp_dup_pco
+mm_gdbus_modem3gpp_get_initial_eps_bearer
+mm_gdbus_modem3gpp_dup_initial_eps_bearer
 <SUBSECTION Methods>
 mm_gdbus_modem3gpp_call_register
 mm_gdbus_modem3gpp_call_register_finish
@@ -1786,6 +1794,7 @@ mm_gdbus_modem3gpp_set_registration_state
 mm_gdbus_modem3gpp_set_subscription_state
 mm_gdbus_modem3gpp_set_eps_ue_mode_operation
 mm_gdbus_modem3gpp_set_pco
+mm_gdbus_modem3gpp_set_initial_eps_bearer
 <SUBSECTION Standard>
 MM_GDBUS_IS_MODEM3GPP
 MM_GDBUS_MODEM3GPP