ofproto: Handle flow installation and eviction in upcall.

ofproto: Handle flow installation and eviction in upcall.

This patch moves flow installation and eviction from ofproto-dpif and
the main thread, into ofproto-dpif-upcall.  This performs
significantly better (approximately 2x TCP_CRR improvement), and
allows ovs-vswitchd to maintain significantly larger datapath flow
tables.  On top of that, it significantly simplifies the code,
retiring "struct facet" and friends.

Signed-off-by: Ethan Jackson <ethan@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>