Ethernet and WiFi UDP reference correction

The ethernet and wifi shield libraries have an error in the UDP.begin(port) function descriptions. The functions do return a value. This is from WiFiUdp.h and same in EthernetUdp.h.

  virtual uint8_t begin(uint16_t); // initialize, start listening on specified port. Returns 1 if successful, 0 if there are no sockets available to use

The Returns sections should show this.

Returns 1 on success or 0 on fail (byte)