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 <abdelrahmanfekry375@gmail.com>
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
Link: https://patch.msgid.link/20250624150923.40590-1-abdelrahmanfekry375@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: AbdelrahmanYousryy