Previous too pessimistic estimation made completely impossible to send
packets with many segments (more than 100 with minimum Tx ring size).
Fixes: 8b00f426eb66 ("net/sfc: implement EF10 native Tx datapath")
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Andrew Lee <alee@solarflare.com>
b69862719e