network: Need to free formatted addr in networkDnsmasqConfContents

Commit id '0b6336c2' formatted the 'addr', but didn't VIR_FREE it.

Found by Coverity.

src/network/bridge_driver.c

@@ -969,6 +969,7 @@ networkDnsmasqConfContents(virNetworkObjPtr network,
                 if (!addr)
                     goto cleanup;
                 virBufferAsprintf(&configbuf, "%s\n", addr);
+                VIR_FREE(addr);
             } else {
                 /* "don't forward requests for this domain" */
                 virBufferAddLit(&configbuf, "#\n");