nfp: xsk: add configuration check for XSK socket chunk size

In preparation for adding AF_XDP support add a configuration check to
make sure the buffer size can not be set to a larger value then the XSK
socket chunk size.

Signed-off-by: Niklas Söderlund <niklas.soderlund@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>