ofproto-dpif-xlate: Make xlate_actions() caller supply flow_wildcards.

ofproto-dpif-xlate: Make xlate_actions() caller supply flow_wildcards.

Until now, struct xlate_out has embedded a struct flow_wildcards, which
xlate_actions() filled in during the flow translation process (unless this
was disabled with xin->skip_wildcards, which in classifier microbenchmarks
saves significant time).  This commit removes the embedded flow_wildcards
and 'skip_wildcards', instead putting a pointer to a flow_wildcards into
struct xlate_in, for a caller to fill in with a pointer to its own
structure if desired.

One reason for this change is performance.  Until now, the userspace slow
path has done a full copy of a struct flow_wildcards for each upcall in
upcall_cb().  This commit eliminates that copy.  I don't know whether this
has a measurable performance impact; it may, because struct flow copies
had a noticeable cost in slow-path stress tests even when struct flow was
half its current size.

This commit also eliminates a large data structure from struct xlate_out,
reducing the cost of the initialization of that structure at the beginning
of xlate_actions().  However, there is more size reduction to come in
later commits.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Jarno Rajahalme <jrajahalme@nicira.com>