sfxge(4): use MCDIv2 for requests with too long response

Use MCDIv2 for requests with a response size too long for MCDIv1.

Required for MC_CMD_MAC_STATS to reports the stats without using DMA.

Submitted by: Mark Spender <mspender at solarflare.com>
Sponsored by: Solarflare Communications, Inc.
Differential Revision: https://reviews.freebsd.org/D18103