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

With recent changes to smb.conf[1] smb2.session.reauth4 is expected to
fail on XFS. Refer [1] for more deails.

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

Signed-off-by: Anoop C S <[email protected]>

Author: anoopcs9

testcases/smbtorture/selftest/flapping.xfs

@@ -5,3 +5,6 @@
 # Ignore due to lack of proper multichannel setup.
 ^samba3.smb2.session.bind2
 ^samba3.smb2.session.two_logoff
+
+# https://github.com/samba-in-kubernetes/sit-environment/pull/109
+samba3.smb2.session.reauth4