doc: Rename AT command files

Renaming AT command files from XXX_AT_commands.rst to at_xxx.rst.

Signed-off-by: Tommi Rantanen <tommi.rantanen@nordicsemi.no>

Author: trantanen

doc/app/CARRIER_AT_commands.rst doc/app/at_carrier.rstdoc/app/CARRIER_AT_commands.rst renamed to doc/app/at_carrier.rst

@@ -34,14 +34,14 @@ The modem specific AT commands are documented in the `nRF91x1 AT Commands Refere
    :maxdepth: 2
    :caption: Subpages:
 
-   Generic_AT_commands
-   CMUX_AT_commands
-   FOTA_AT_commands
-   GNSS_AT_commands
-   ICMP_AT_commands
-   CARRIER_AT_commands
-   MQTT_AT_commands
-   NRFCLOUD_AT_commands
-   PPP_AT_commands
-   SMS_AT_commands
-   SOCKET_AT_commands
+   at_generic
+   at_cmux
+   at_fota
+   at_gnss
+   at_icmp
+   at_carrier
+   at_mqtt
+   at_nrfcloud
+   at_ppp
+   at_sms
+   at_socket

doc/app/CMUX_AT_commands.rst doc/app/at_cmux.rstdoc/app/CMUX_AT_commands.rst renamed to doc/app/at_cmux.rst

@@ -263,7 +263,7 @@ Syntax
 Response syntax
 ~~~~~~~~~~~~~~~
 
-.. include:: GNSS_AT_commands.rst
+.. include:: at_gnss.rst
    :start-after: sm_gps_status_notif_start
    :end-before: sm_gps_status_notif_end
 

doc/app/AT_commands.rst doc/app/at_commands.rstdoc/app/AT_commands.rst renamed to doc/app/at_commands.rst

@@ -168,7 +168,7 @@ Syntax
 Response syntax
 ~~~~~~~~~~~~~~~
 
-.. include:: PPP_AT_commands.rst
+.. include:: at_ppp.rst
    :start-after: sm_ppp_status_notif_start
    :end-before: sm_ppp_status_notif_end