PFS: Bump NAMELEN and don't require clients to be sleepable

• debugfs consumers expect to be able to export names more than 48 characters

• debugfs consumers expect to be able to hold locks across calls and are able to handle allocation failures

Reviewed by: hps@
MFC after: 1 week
Sponsored by: iX Systems
Differential Revision: https://reviews.freebsd.org/D19256