selftest: enable kernel change notifications in the fileserver environment

selftest: enable kernel change notifications in the fileserver environment

This environment is currently not used for any test in the smb2
testsuite, so this change doesn't affect any existing test.

A subsequent commit will add a test for change notifications with kernel
change notify enabled. It verifies a bug (this one) that only crops up
in such a setup and causes rename events to get lost.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=12903

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>