sysparam: split the key into a name-space and name.

This is largely to aid compatibility with other non-volatile stores
that have limited sized names but support a name space. This might
open a path to more compact storage of the key names although that is
not implemented here.

lwip/esp_interface.c

@@ -365,7 +365,7 @@ ethernetif_init(struct netif *netif)
     /* Initialize interface hostname */
     char *hostname = NULL;
     /* Disabled for now as there were reports of crashes here, sysparam issues */
-    /* sysparam_get_string("hostname", &hostname); */
+    /* sysparam_get_string("wificfg", "hostname", &hostname); */
     if (hostname && strlen(hostname) == 0) {
         free(hostname);
         hostname = NULL;