Backport esp8266#7586

Author: Jason2866

cores/esp8266/IPAddress.h

@@ -141,6 +141,8 @@ class IPAddress: public Printable {
 
         virtual size_t printTo(Print& p) const;
         String toString() const;
+ 
+        void clear();
 
         /*
                 check if input string(arg) is a valid IPV4 address or not.