fix build with musl

package/busybox/patches/015-path_h_musl.patch

@@ -0,0 +1,11 @@
+diff -Nur busybox-1.20.2.orig/networking/ifplugd.c busybox-1.20.2/networking/ifplugd.c
+--- busybox-1.20.2.orig/networking/ifplugd.c	2012-07-02 16:08:25.000000000 +0200
++++ busybox-1.20.2/networking/ifplugd.c	2013-09-22 11:43:24.000000000 +0200
+@@ -34,6 +34,7 @@
+ #include "libbb.h"
+ 
+ #include "fix_u32.h"
++#include <paths.h>
+ #include <linux/if.h>
+ #include <linux/mii.h>
+ #include <linux/ethtool.h>