Modify ring header data split and jumbo parameters to account
for the fact that the design for XDP multibuffer puts close to
the first 4k of data in a page and the remaining portions of
the packet go in the aggregation ring.

v3: Simplified code around initial buffer size calculation
Signed-off-by: Andy Gospodarek <gospo@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>