audit: enforce op for string fields

The field operator is ignored on several string fields.  WATCH, DIR,
PERM and FILETYPE field operators are completely ignored and meaningless
since the op is not referenced in audit_filter_rules().  Range and
bitwise operators are already addressed in ghak73.

Honour the operator for WATCH, DIR, PERM, FILETYPE fields as is done in
the EXE field.

Please see github issue
https://github.com/linux-audit/audit-kernel/issues/114



Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>