devel/mdb: Update to a newer snapshot which builds on recent HEAD.

This snapshot includes fixes to build again on HEAD after the OpenZFS
import. It also fixes ::kgrep on HEAD after the changes in r346302.
Finally, it includes debug symbols in shipped binaries to ease future
debugging.

Tested by: gallatin
Approved by: kevans (ports)
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D27427