Improve error checking to avoid a caller overflowing the MCDI
request buffer if the requested TXQ size was excessively large.
Coverity issue: 1305527
Fixes: e7cd430c864f ("net/sfc/base: import SFN7xxx family support")
CC: stable@dpdk.org
Signed-off-by: Andy Moreton <amoreton@solarflare.com>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>