Initialize SoftAP DhcpServer object on demand (#8546)

* Initialize SoftAP DhcpServer object on demand

Remove dependency on global ctor, and just construct the object when
someone asks us to do it. Only dependency right now is netif_git, which
is expected to be initialized by the lwip code some time before
dhcps_start happens.

Removing ip_info from begin(), since we never reference later on.
Also removing the specific check for netif id and simplify the ctors.

Update tests and recover old nonos-sdk dhcps functions that were not implemented.

* nonos helpers have a separate header

* wifi ap needs this anyway, simplify sketch includes

* missing example

* existing name :/

* trying to fix header dependency

* restyle

* not a c header

* no need to init

* move dhcp server getter to WiFi

more... arduino'ish? we ahve object as namespace, plus everything else
related to softAP is there
redundant includes, redundant mock impl (out-of-scope here to fix)

* ...move things back, still expose as WiFi method

* review fix

* include -nonos header in wifi lib though

* no more lwip include

* style

* need mock dhcpserver instance

libraries/ESP8266WiFi/examples/StaticLease/StaticLease.ino

@@ -4,7 +4,6 @@
 #include <ESP8266WiFi.h>
 #include <WiFiClient.h>
 #include <ESP8266WebServer.h>
-#include <LwipDhcpServer.h>
 
 /* Set these to your desired credentials. */
 const char *ssid = "ESPap";
@@ -76,8 +75,9 @@ void setup() {
      ...
      any client not listed will use next IP address available from the range (here 192.168.0.102 and more)
   */
-  dhcpSoftAP.add_dhcps_lease(mac_CAM);  // always 192.168.0.100
-  dhcpSoftAP.add_dhcps_lease(mac_PC);   // always 192.168.0.101
+  auto &dhcpServer = WiFi.softAPDhcpServer();
+  dhcpServer.add_dhcps_lease(mac_CAM);  // always 192.168.0.100
+  dhcpServer.add_dhcps_lease(mac_PC);   // always 192.168.0.101
   /* Start Access Point. You can remove the password parameter if you want the AP to be open. */
   WiFi.softAP(ssid, password);
   Serial.print("AP IP address: ");