mb-applet-wireless: fix undefined reference to `log' and `lrint'

mb-applet-wireless.o: In function `update_wireless':
.. matchbox-panel-0.9.3/applets/mb-applet-wireless.c:143: undefined reference to `log'
.. matchbox-panel-0.9.3/applets/mb-applet-wireless.c:143: undefined reference to `lrint'

Signed-off-by: Jean-Paul Etienne <fractalclone@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
[arnout: add description and Signed-off-by]
---
diff -rup matchbox-panel-0.9.3.orig/applets/Makefile.in matchbox-panel-0.9.3/applets/Makefile.in
--- matchbox-panel-0.9.3.orig/applets/Makefile.in	2015-01-23 00:16:47.594850985 +0100
+++ matchbox-panel-0.9.3/applets/Makefile.in	2015-01-23 00:15:18.458694947 +0100
@@ -198,7 +198,7 @@ WANT_SMALL_ICONS_FALSE = @WANT_SMALL_ICO
 WANT_SMALL_ICONS_TRUE = @WANT_SMALL_ICONS_TRUE@
 WANT_WIFI_FALSE = @WANT_WIFI_FALSE@
 WANT_WIFI_TRUE = @WANT_WIFI_TRUE@
-WIRELESS_LIBS = @WIRELESS_LIBS@
+WIRELESS_LIBS = @WIRELESS_LIBS@ -lm
 XGETTEXT = @XGETTEXT@
 ac_ct_CC = @ac_ct_CC@
 ac_ct_STRIP = @ac_ct_STRIP@
diff -rup matchbox-panel-0.9.3.orig/applets/mb-applet-wireless.c matchbox-panel-0.9.3/applets/mb-applet-wireless.c
--- matchbox-panel-0.9.3.orig/applets/mb-applet-wireless.c	2015-01-23 00:16:31.531822865 +0100
+++ matchbox-panel-0.9.3/applets/mb-applet-wireless.c	2015-01-23 00:03:43.067563827 +0100
@@ -50,6 +50,8 @@
 
 #endif
 
+#include <math.h>
+
 #ifdef MB_HAVE_PNG
 #define IMG_EXT "png"
 #else