htb: fix sign extension bug

When userspace passes a large priority value
the assignment of the unsigned value hopt->prio
to  signed int cl->prio causes cl->prio to become negative and the
comparison is with TC_HTB_NUMPRIO is always false.

The result is that HTB crashes by referencing outside
the array when processing packets. With this patch the large value
wraps around like other values outside the normal range.

See: https://bugzilla.kernel.org/show_bug.cgi?id=60669



Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>