net: netcp: fix unused interface rx buffer size configuration

Prior to this patch, rx buffer size for each rx queue
of an interface is configurable through dts bindings.
But for an interface, the first rx queue's rx buffer
size is always the usual MTU size (plus usual overhead)
and page size for the remaining rx queues (if they are
enabled by specifying a non-zero rx queue depth dts
binding of the corresponding interface).  This patch
removes the rx buffer size configuration capability.

Signed-off-by: WingMan Kwok <w-kwok2@ti.com>
Acked-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>