IPAddress updates (#5409)

* restore definition of ip_addr (=ipv4_addr) when IPv6 is not enabled

* overload IPAddress:operator == and != to avoid ambiguousness

* brings lwIP's INADDR_NONE (which is IPv4 255.255.255.255, suposed to be invalid address but it is)

* inet_aton is a lwIP define, rename Ethernet DNS implementation of this to prevent name collision
that's because IPAddress now includes lwip/inet.h

Author: d-a-v

cores/esp8266/IPAddress.h

@@ -38,9 +38,12 @@
 #define IP4_ADDR_ANY4 IPADDR_ANY
 #define IPADDR4_INIT(x) { x }
 #define CONST /* nothing: lwIP-v1 does not use const */
-#else
+#else // lwIP-v2+
 #define CONST const
-#endif
+#if !LWIP_IPV6
+#define ip_addr ipv4_addr
+#endif // !LWIP_IPV6
+#endif // lwIP-v2+
 
 // A class to make it easier to handle and pass around IP addresses
 // IPv6 update:
@@ -96,9 +99,15 @@ class IPAddress: public Printable {
         bool operator==(uint32_t addr) const {
             return isV4() && v4() == addr;
         }
+        bool operator==(u32_t addr) const {
+            return isV4() && v4() == addr;
+        }
         bool operator!=(uint32_t addr) const {
             return !(isV4() && v4() == addr);
         }
+        bool operator!=(u32_t addr) const {
+            return !(isV4() && v4() == addr);
+        }
         bool operator==(const uint8_t* addr) const;
 
         // Overloaded index operator to allow getting and setting individual octets of the address
@@ -193,6 +202,7 @@ class IPAddress: public Printable {
 
 extern CONST IPAddress IPNoAddress;
 
-#include <AddrList.h>
+#include <lwip/inet.h> // bring definition of INADDR_NONE
+#include <AddrList.h>  // bring interface iterator
 
 #endif

libraries/Ethernet/src/Dns.cpp

@@ -55,7 +55,7 @@ void DNSClient::begin(const IPAddress& aDNSServer)
 }
 
 
-int DNSClient::inet_aton(const char* aIPAddrString, IPAddress& aResult)
+int DNSClient::inet_aton_ethlib(const char* aIPAddrString, IPAddress& aResult)
 {
     // See if we've been given a valid IP address
     const char* p =aIPAddrString;
@@ -120,7 +120,7 @@ int DNSClient::getHostByName(const char* aHostname, IPAddress& aResult)
     int ret =0;
 
     // See if it's a numeric IP address
-    if (inet_aton(aHostname, aResult))
+    if (inet_aton_ethlib(aHostname, aResult))
     {
         // It is, our work here is done
         return 1;

libraries/Ethernet/src/Dns.h

@@ -19,7 +19,7 @@ class DNSClient
         @result 1 if aIPAddrString was successfully converted to an IP address,
                 else error code
     */
-    int inet_aton(const char *aIPAddrString, IPAddress& aResult);
+    int inet_aton_ethlib(const char *aIPAddrString, IPAddress& aResult);
 
     /** Resolve the given hostname to an IP address.
         @param aHostname Name to be resolved