net/sched: cls_flower: Use a proper mask value for enc key id parameter

The current code use the encapsulation key id value as the mask of that
parameter which is wrong. Fix that by using a full mask.

Fixes: bc3103f1 ('net/sched: cls_flower: Classify packet in ip tunnels')
Signed-off-by: Hadar Hen Zion <hadarh@mellanox.com>
Acked-by: Amir Vadai <amir@vadai.me>
Signed-off-by: David S. Miller <davem@davemloft.net>