Add MacAddress string constructor (espressif#9400)

* Add MacAddress string constructor * Change implementation

Author: lucasssvaz

cores/esp32/MacAddress.cpp

@@ -28,6 +28,10 @@ MacAddress::MacAddress(const char *macstr){
  fromString(macstr);
 }
 
+MacAddress::MacAddress(const String &macstr){
+ fromString(macstr.c_str());
+}
+
 MacAddress::MacAddress(uint8_t b1, uint8_t b2, uint8_t b3, uint8_t b4, uint8_t b5, uint8_t b6) {
  _type = MAC6;
  memset(_mac.bytes, 0, sizeof(_mac.bytes));

cores/esp32/MacAddress.h

@@ -54,6 +54,7 @@ class MacAddress : public Printable {
  MacAddress(const uint8_t *macbytearray) : MacAddress(MAC6, macbytearray) {}
 
  MacAddress(const char *macstr);
+ MacAddress(const String &macstr);
 
  virtual ~MacAddress() {}