ada: Add support for binding to a specific network interface controller.

gcc/ada/

	* s-oscons-tmplt.c: Add support for SO_BINDTODEVICE constant.
	* libgnat/g-socket.ads (Set_Socket_Option): Handle SO_BINDTODEVICE option.
	(Get_Socket_Option): Handle SO_BINDTODEVICE option.
	* libgnat/g-socket.adb: Likewise.
	(Get_Socket_Option): Handle the case where IF_NAMESIZE is not defined
	and so equal to -1.