chan_dahdi: add missing include.

After some definitions have been moved to asterisk/mwi.h the files
channels/chan_dahdi.h channels/sig_pri.c are missing this new
include.

ASTERISK-28427 #close

Change-Id: Ia8cc595eeda653324643f40dcd9799d4c3f0ac91

channels/chan_dahdi.h

@@ -39,6 +39,7 @@
 #include "asterisk/channel.h"
 #include "asterisk/dsp.h"
 #include "asterisk/app.h"
+#include "asterisk/mwi.h"
 
 #if defined(__cplusplus) || defined(c_plusplus)
 extern "C" {

channels/sig_pri.c

@@ -101,6 +101,7 @@
 #include "asterisk/options.h"
 #include "asterisk/pbx.h"
 #include "asterisk/app.h"
+#include "asterisk/mwi.h"
 #include "asterisk/file.h"
 #include "asterisk/callerid.h"
 #include "asterisk/say.h"