[CIFS] Fix cifsd so shuts down when signing fails during mount

Fixes two problems:
1) we dropped down to negotiating lanman if we did not recognize the
mechanism (krb5 e.g.)
2) we did not stop cifsd (thus will fail when doing rmod cifs with
slab free errors) when we fail tcon but have a bad session (which is
the case in which signing is required but we don't allow signing on
the client)

It also turns on extended security flag in the header when passing
"sec=krb5" on mount command (although kerberos support is not done of
course)

Acked-by: Jeff Layton <jlayton@redhat.com>
CC: Shaggy <shaggy@us.ibm.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 3fb046b..fbde55c 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -90,7 +90,8 @@
 };
 
 enum securityEnum {
-	LANMAN = 0,             /* Legacy LANMAN auth */
+	PLAINTXT = 0, 		/* Legacy with Plaintext passwords */
+	LANMAN,			/* Legacy LANMAN auth */
 	NTLM,			/* Legacy NTLM012 auth with NTLM hash */
 	NTLMv2,			/* Legacy NTLM auth with NTLMv2 hash */
 	RawNTLMSSP,		/* NTLMSSP without SPNEGO */
@@ -499,6 +500,7 @@
 
 #define   CIFSSEC_DEF  CIFSSEC_MAY_SIGN | CIFSSEC_MAY_NTLM | CIFSSEC_MAY_NTLMV2
 #define   CIFSSEC_MAX  CIFSSEC_MUST_SIGN | CIFSSEC_MUST_NTLMV2
+#define   CIFSSEC_AUTH_MASK (CIFSSEC_MAY_NTLM | CIFSSEC_MAY_NTLMV2 | CIFSSEC_MAY_LANMAN | CIFSSEC_MAY_PLNTXT | CIFSSEC_MAY_KRB5)
 /*
  *****************************************************************
  * All constants go here