cifs: fix MUST SecurityFlags filtering

If CONFIG_CIFS_WEAK_PW_HASH is not set, CIFSSEC_MUST_LANMAN
and CIFSSEC_MUST_PLNTXT is defined as 0.

When setting new SecurityFlags without any MUST flags,
your flags would be overwritten with CIFSSEC_MUST_LANMAN (0).
Signed-off-by: Niklas Cassel <niklass@axis.com>
Signed-off-by: Steve French <steve.french@primarydata.com>

fs/cifs/cifs_debug.c

@@ -606,9 +606,11 @@ cifs_security_flags_handle_must_flags(unsigned int *flags)
 		*flags = CIFSSEC_MUST_NTLMV2;
 	else if ((*flags & CIFSSEC_MUST_NTLM) == CIFSSEC_MUST_NTLM)
 		*flags = CIFSSEC_MUST_NTLM;
-	else if ((*flags & CIFSSEC_MUST_LANMAN) == CIFSSEC_MUST_LANMAN)
+	else if (CIFSSEC_MUST_LANMAN &&
+		 (*flags & CIFSSEC_MUST_LANMAN) == CIFSSEC_MUST_LANMAN)
 		*flags = CIFSSEC_MUST_LANMAN;
-	else if ((*flags & CIFSSEC_MUST_PLNTXT) == CIFSSEC_MUST_PLNTXT)
+	else if (CIFSSEC_MUST_PLNTXT &&
+		 (*flags & CIFSSEC_MUST_PLNTXT) == CIFSSEC_MUST_PLNTXT)
 		*flags = CIFSSEC_MUST_PLNTXT;
 
 	*flags |= signflags;