fix testing IPAddress validity (#5684)

* fix testing IPAddress validity (operator bool())
* +add new operator=
* +cast to u32_t
* + operator >>

Author: d-a-v

cores/esp8266/IPAddress.h

@@ -87,13 +87,15 @@ class IPAddress: public Printable {
 
         // Overloaded cast operator to allow IPAddress objects to be used where a pointer
         // to a four-byte uint8_t array is expected
-        operator uint32_t() const {
-            return isV4()? v4(): (uint32_t)0;
-        }
+        operator uint32_t() const { return isV4()? v4(): (uint32_t)0; }
+        operator uint32_t()       { return isV4()? v4(): (uint32_t)0; }
+        operator u32_t()    const { return isV4()? v4():    (u32_t)0; }
+        operator u32_t()          { return isV4()? v4():    (u32_t)0; }
 
-        // the above uint32_t() cast can be ambiguous
-        // if gcc complains, use instead isSet() or v4() according to what's relevant
         bool isSet () const;
+        operator bool () const { return isSet(); } // <-
+        operator bool ()       { return isSet(); } // <- both are needed
+
         // generic IPv4 wrapper to uint32-view like arduino loves to see it
         const u32_t& v4() const { return ip_2_ip4(&_ip)->addr; } // for raw_address(const)
               u32_t& v4()       { return ip_2_ip4(&_ip)->addr; }
@@ -118,6 +120,10 @@ class IPAddress: public Printable {
         }
         bool operator==(const uint8_t* addr) const;
 
+        int operator>>(int n) const {
+            return isV4()? v4() >> n: 0;
+        }
+
         // Overloaded index operator to allow getting and setting individual octets of the address
         uint8_t operator[](int index) const {
             return isV4()? *(raw_address() + index): 0;
@@ -155,6 +161,9 @@ class IPAddress: public Printable {
         IPAddress(const ipv4_addr& fw_addr)   { setV4(); v4() = fw_addr.addr; }
         IPAddress(const ipv4_addr* fw_addr)   { setV4(); v4() = fw_addr->addr; }
 
+        IPAddress& operator=(const ipv4_addr& fw_addr)   { setV4(); v4() = fw_addr.addr;  return *this; }
+        IPAddress& operator=(const ipv4_addr* fw_addr)   { setV4(); v4() = fw_addr->addr; return *this; }
+
         operator       ip_addr_t () const { return  _ip; }
         operator const ip_addr_t*() const { return &_ip; }
         operator       ip_addr_t*()       { return &_ip; }
@@ -169,6 +178,9 @@ class IPAddress: public Printable {
         IPAddress(const ip_addr_t& lwip_addr) { ip_addr_copy(_ip, lwip_addr); }
         IPAddress(const ip_addr_t* lwip_addr) { ip_addr_copy(_ip, *lwip_addr); }
 
+        IPAddress& operator=(const ip_addr_t& lwip_addr) { ip_addr_copy(_ip, lwip_addr); return *this; }
+        IPAddress& operator=(const ip_addr_t* lwip_addr) { ip_addr_copy(_ip, *lwip_addr); return *this; }
+
         uint16_t* raw6()
         {
             setV6();