net_sched: red: Avoid illegal values

commit 8afa10cbe281b10371fee5a87ab266e48d71a7f9 upstream.

Check the qmin & qmax values doesn't overflow for the given Wlog value.
Check that qmin <= qmax.

Fixes: a783474591f2 ("[PKT_SCHED]: Generic RED layer")
Signed-off-by: Nogah Frankel <nogahf@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2:
 - Drop changes in sch_sfq
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>