Fix compilation errors when using gcc-7.2.0 for the crosstool-ng toolchain

* Change snprintf for strlcat does not complain w/gcc7.2.0 and it is safer, thanks @projectgus
* Use proper quotes for character literals

Merges espressif/esp-idf#1163


* Original commit: espressif/esp-idf@519edc3

Author: brainstorm

components/mdns/mdns.c

@@ -569,7 +569,8 @@ static const uint8_t * _mdns_read_fqdn(const uint8_t * packet, const uint8_t * s
                     && (strcmp(buf, MDNS_DEFAULT_DOMAIN) != 0)
                     && (strcmp(buf, "ip6") != 0)
                     && (strcmp(buf, "in-addr") != 0)) {
-                snprintf((char*)name, MDNS_NAME_BUF_LEN, "%s.%s", name->host, buf);
+                strlcat(name->host, ".", sizeof(name->host));
+                strlcat(name->host, buf, sizeof(name->host));
             } else if (strcmp(buf, MDNS_SUB_STR) == 0) {
                 name->sub = 1;
             } else {