net: rmnet: Use section heading markup for packet format subsections

Format subsections of "Packet format" section as reST subsections.

Link: https://lore.kernel.org/linux-doc/[e-mail]/
Suggested-by: Simon Horman <[e-mail]>
Signed-off-by: Bagas Sanjaya <[e-mail]>
Reviewed-by: Randy Dunlap <[e-mail]>
Tested-by: Randy Dunlap <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

Documentation/networking/device_drivers/cellular/qualcomm/rmnet.rst

···
 ================
 
 a. MAP packet v1 (data / control)
+---------------------------------
 
 MAP header fields are in big endian format.
 
···
 length.
 
 b. Map packet v4 (data / control)
+---------------------------------
 
 MAP header fields are in big endian format.
 
···
 Checksum value, indicates the checksum computed.
 
 c. MAP packet v5 (data / control)
+---------------------------------
 
 MAP header fields are in big endian format.
 
···
 length.
 
 d. Checksum offload header v5
+-----------------------------
 
 Checksum offload header fields are in big endian format.
 
···
 
 Reserved bits must be zero when sent and ignored when received.
 
-e. MAP packet v1/v5 (command specific)::
+e. MAP packet v1/v5 (command specific)
+--------------------------------------
+
+Packet format::
 
     Bit             0             1         2-7      8 - 15           16 - 31
     Function   Command         Reserved     Pad   Multiplexer ID    Payload length
···
 = ==========================================
 
 f. Aggregation
+--------------
 
 Aggregation is multiple MAP packets (can be data or command) delivered to
 rmnet in a single linear skb. rmnet will process the individual