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

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/aO_MefPIlQQrCU3j@horms.kernel.org/
Suggested-by: Simon Horman <horms@kernel.org>
Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://patch.msgid.link/20251022025456.19004-2-bagasdotme@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>