lib: utils: Introduce parse_one_of_deprecated()

lib: utils: Introduce parse_one_of_deprecated()

The function parse_one_of() currently uses matches() for string comparison
under the hood. Extending matches()-based parsers is tricky, because newly
added matches might change the way strings are parsed, if the newly-added
string shares a prefix with a string that is matched later in the code.

In this patch, introduce a new function, parse_one_of_deprecated(). This
will be currently synonymous with parse_one_of(), however the latter will
change behavior in the next patch.

Use the new function for parsing of the macsec "validate" option. The
reason is that the valid strings for that option are "disabled", "check"
and "strict". It is not hard to see how "disabled" could be misspelled as
"disable", and be baked in some script in this form.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: David Ahern <dsahern@kernel.org>