net: ethernet: Make NET_VENDOR_AURORA default to yes

Enabling NET_VENDOR_* Kconfig options does not directly affect the
kernel build.  Hence NET_VENDOR_AURORA should default to yes, like other
NET_VENDOR_* options.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: David S. Miller <davem@davemloft.net>