[NET]: Add missing include to linux/netdevice.h

linux/etherdevice.h can't be included standalone at the moment, which
is required in order to sort the header files in the recommended
alphabetic order. This patch fixes that and is needed to build spider_net.

Signed-off-by: Arnd Bergmann <arndb@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>