ofproto-dpif-xlate: Fix handling of write_actions(group(5),output(10)).

ofproto-dpif-xlate: Fix handling of write_actions(group(5),output(10)).

This keeps actset_output as OFPP_UNSET in the special case where a single
write_actions() contains a group action followed by an output action.  The
presumably more common case where instructions in separate action lists
contained output and group actions was already properly handled.

Without the fix added by this commit, the test case as updated by this
commit fails.

Found by inspection.

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