flapping.cephfs: Add smb2.session.reauth4 as knownfail

With recent changes to smb.conf[1], smb2.session.reauth4 is expected to
fail on CephFS kclient method. Refer [1] for more details.

[1] samba-in-kubernetes/sit-environment#109

Signed-off-by: Anoop C S <anoopcs@cryptolab.net>

testcases/smbtorture/selftest/flapping.cephfs

@@ -16,3 +16,7 @@ samba3.smb2.timestamps.time_t_10000000000
 samba3.smb2.timestamps.time_t_-1
 samba3.smb2.timestamps.time_t_-2
 samba3.smb2.timestamps.time_t_1968
+
+# https://github.com/samba-in-kubernetes/sit-environment/pull/109
+# Note: CephFS(vfs) successfully completes smb2.session.reauth4.
+samba3.smb2.session.reauth4