ofproto: Remove per-flow miss hash table from upcall handler.

The upcall handler keeps a hash table which hashes flow to a list
of corresponding packets.  This used to be necessary as packets with
the same flow had similar actions and calculating actions used to be
a performance bottleneck.  Now that userspace action calculation
performance has improved, there is no need for this hash map.

This patch removes this hash map and each packet has its own upcall.

Signed-off-by: Ryan Wilson <wryan@nicira.com>
Acked-by: Alex Wang <alexw@nicira.com>