ofproto-dpif-upcall: Fix a free of uninitialized memory.

ofproto-dpif-upcall: Fix a free of uninitialized memory.

On current master, when 'upcall_receive()' returns error, the
ofpbuf 'upcall->put_actions' is uninitialized.  In some usecase,
the failure of 'upcall_receive()' will cause uninitialize of
'upcall->put_actions' and free of uninitialized pointer.

This commit fixes the issue by making the caller not conduct
the uninitialize of the 'upcall' when there is error.

Found by inspection.

Signed-off-by: Alex Wang <alexw@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>