11227 smb code needs smatch fixes

@@ -17,10 +17,11 @@
  * information: Portions Copyright [yyyy] [name of copyright owner]
  *
  * CDDL HEADER END
  */
 /*
+ * Copyright 2019 Joyent, Inc.
  * Copyright 2015 Nexenta Systems, Inc.  All rights reserved.
  * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
  * Use is subject to license terms.
  */
 /*

@@ -231,11 +232,12 @@
  * Place the successor, if any, in nn.
  */
 #define MFREE(m, nn) \
         { \
                 if ((m)->m_flags & M_EXT) {                 \
-                        (*((m)->m_ext.ext_ref))((m)->m_ext.ext_buf,     \
+                        (void) (*((m)->m_ext.ext_ref))                  \
+                            ((m)->m_ext.ext_buf,                        \
                             (m)->m_ext.ext_size, -1);                   \
                         (m)->m_ext.ext_buf = 0;                         \
                 }                                                       \
                 (nn) = (m)->m_next;                                     \
                 (m)->m_next = 0;                                        \