ynl: ensure exact-len value is resolved

ynl: ensure exact-len value is resolved

For type String and Binary we are currently usinig the exact-len
limit value as is without attempting any name resolution.
However, the spec may specify the name of a constant rather than an
actual value, which would result in using the constant name as is
and thus break the policy.

Ensure the limit value is passed to get_limit(), which will always
attempt resolving the name before printing the policy rule.

Signed-off-by: Antonio Quartulli <a@unstable.cc>
Link: https://lore.kernel.org/r/20240510232202.24051-1-a@unstable.cc
Signed-off-by: Jakub Kicinski <kuba@kernel.org>