ofproto-dpif: Fix memory leak in handle_flow_miss().

Every xlate_actions() needs a corresponding xlate_out_uninit(), but the
call in handle_flow_miss() lacked one.  struct xlate_out has a built-in
256-byte actions stub, so the bug only showed up for lots of actions.

Bug #19198.
Reported-by: Ronald Lee <ronaldlee@vmware.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Justin Pettit <jpettit@nicira.com>