Include <sys/param.h> for roundup() declaration with musl libc

--- dns.c	2013-06-03 16:03:15.000000000 +0200
+++ dns.c	2015-08-07 14:53:01.499713464 +0200
@@ -33,6 +33,7 @@
  */
 
 #include <sys/types.h>
+#include <sys/param.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
 #include <arpa/nameser.h>