This currently has no effect: We don't include AEAD algorithms in the default ESP proposal, as we don't know if it is supported by the backend. But as we hopefully get an algorithm query mechanism on kernel interfaces some day, we add the appropriate functionality nonetheless.
Handling the result for enum_from_name() is difficult, as checking for negative return values requires a cast if the enum type is unsigned. The new signature clearly differentiates lookup result from lookup value. Further, this actually allows to convert real -1 enum values, which could not be distinguished from "not-found" and the -1 return value. This also fixes several clang warnings where enums are unsigned.