mi_fifo: Add a default for "fifo_name"

This is useful for test automation, since now we only have to load
"mi_fifo.so" programatically in order to offer MI communication.

Author: liviuchircu

modules/mi_fifo/doc/mi_fifo_admin.xml

@@ -96,14 +96,14 @@
 		</para>
 		<para>
 		<emphasis>
-			Default value is NONE.
+			Default value is "/tmp/opensips_fifo".
 		</emphasis>
 		</para>
 		<example>
 		<title>Set <varname>fifo_name</varname> parameter</title>
 		<programlisting format="linespecific">
 ...
-modparam("mi_fifo", "fifo_name", "/tmp/opensips_fifo")
+modparam("mi_fifo", "fifo_name", "/tmp/opensips_b2b_fifo")
 ...
 </programlisting>
 		</example>

modules/mi_fifo/mi_fifo.c

@@ -49,7 +49,7 @@ static int mi_destroy(void);
 
 /* FIFO server vars */
 /* FIFO name */
-static char *mi_fifo = 0;
+static char *mi_fifo = "/tmp/opensips_fifo";
 /* dir where reply fifos are allowed */
 static char *mi_fifo_reply_dir = DEFAULT_MI_REPLY_DIR;
 static int  mi_fifo_uid = -1;