To support Ethernet2.h library, this should be "ethernet_h"

[yardov]

This line:

https://github.com/marcoschwartz/aREST/blob/bcb3e3583cf75890598bf68612b5c36d324d2dd8/aREST.h#L574

Should include the Ethernet2.h support and thus the variable "ethernet_h" should be also added.... (ethernet_h_ || ethernet_h)

Is there any other reason why this variable was not included but the release 2.7.4 says that is supports Ethernet2?