conf: eliminate redundant VIR_ALLOC of 1st element of network DNS hosts.

virNetworkDNSHostsDefParseXML was calling VIR_ALLOC(def->hosts) if
def->hosts was NULL. This is a waste of time, though, since
VIR_REALLOC_N is called a few lines further down, prior to any use of
def->hosts. (initializing def->nhosts to 0 is also redundant, because
the newly allocated memory will always be cleared to all 0's anyway).

src/conf/network_conf.c

@@ -510,14 +510,6 @@ virNetworkDNSHostsDefParseXML(virNetworkDNSDefPtr def,
     virSocketAddr inaddr;
     int ret = -1;
 
-    if (def->hosts == NULL) {
-        if (VIR_ALLOC(def->hosts) < 0) {
-            virReportOOMError();
-            goto error;
-        }
-        def->nhosts = 0;
-    }
-
     if (!(ip = virXMLPropString(node, "ip")) ||
         (virSocketAddrParse(&inaddr, ip, AF_UNSPEC) < 0)) {
         virNetworkReportError(VIR_ERR_XML_DETAIL,