md: Use a larger buffer for the ident string

With the old size, the string could easily be truncated, resulting in
non-unique identifiers.

PR: 287679
Reported by: Phil Krylov <phil@krylov.eu>
Reviewed by: kib
MFC after: 2 weeks

(cherry picked from commit 5286b96c56ff5aa3c1cee824ab8564f0ffffc381)