Merge pull request #518 from d-a-v/EthernetMaintain

implement arduino API: Ethernet.maintain()

Author: facchinm

Diff for: libraries/Ethernet/src/Ethernet.h

@@ -42,6 +42,14 @@ enum EthernetHardwareStatus {
 
 namespace arduino {
 
+enum {  // compatibility with Arduino ::maintain()
+    DHCP_CHECK_NONE         = 0,
+    DHCP_CHECK_RENEW_FAIL   = 1,
+    DHCP_CHECK_RENEW_OK     = 2,
+    DHCP_CHECK_REBIND_FAIL  = 3,
+    DHCP_CHECK_REBIND_OK    = 4
+};
+
 typedef void *(*voidPrtFuncPtr)(void);
 
 class EthernetClass : public MbedSocketClass {
@@ -107,6 +115,8 @@ class EthernetClass : public MbedSocketClass {
 
   NetworkInterface *getNetwork();
 
+  constexpr static int maintain () { return DHCP_CHECK_NONE; }
+
 private:
   volatile EthernetLinkStatus _currentNetworkStatus = Unknown;
   EthernetInterface net;