docs: net: sysctl documentation cleanup

Add missing default values for networking sysctl parameters and
standardize documentation:
- Use "0 (disabled)" / "1 (enabled)" format consistently
- Fix cipso_rbm_struct_valid -> cipso_rbm_strictvalid typo
- Convert fwmark_reflect description to enabled/disabled terminology
- Document possible values for tcp_autocorking

Also addresses formatting inconsistencies in touched parameters.

Signed-off-by: Abdelrahman Fekry <[email protected]>
Reviewed-by: Bagas Sanjaya <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>

Author: AbdelrahmanYousryy