apparmor: fix documentation mismatches in val_mask_to_str and socket functions

apparmor: fix documentation mismatches in val_mask_to_str and socket functions

This patch fixes kernel-doc warnings:
1. val_mask_to_str:
- Added missing descriptions for `size` and `table` parameters.
- Removed outdated str_size and chrs references.
2. Socket Functions:
- Makes non-null requirements clear for socket/address args.
- Standardizes return values per kernel conventions.
- Adds Unix domain socket protocol details.

These changes silence doc validation warnings and improve accuracy for
AppArmor LSM docs.

Signed-off-by: Peng Jiang <jiang.peng9@zte.com.cn>
Signed-off-by: John Johansen <john.johansen@canonical.com>