Constify 'hostname' and 'service' to various resolver functions.

lib/hostares.c

@@ -259,7 +259,7 @@ CURLcode Curl_wait_for_resolv(struct connectdata *conn,
  * Curl_freeaddrinfo(), nothing else.
  */
 Curl_addrinfo *Curl_getaddrinfo(struct connectdata *conn,
-                                char *hostname,
+                                const char *hostname,
                                 int port,
                                 int *waitp)
 {
@@ -314,7 +314,7 @@ struct namebuf {
  * The input parameters ARE NOT checked for validity but they are expected
  * to have been checked already when this is called.
  */
-Curl_addrinfo *Curl_ip2addr(in_addr_t num, char *hostname, int port)
+Curl_addrinfo *Curl_ip2addr(in_addr_t num, const char *hostname, int port)
 {
   Curl_addrinfo *ai;
   struct hostent *h;