sfxge(4): fix efx_filter_reconfigure parameter type

This caused signed/unsigned errors in some subsequent patches.
The only value passed to this is a uint32_t.

Submitted by: Mark Spender <mspender at solarflare.com>
Sponsored by: Solarflare Communications, Inc.
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D6294