dpif-netdev: Handle uninitialized value error for 'match.wc'

Valgrind reported that match.wc was not initialized, as below:

1176: ofproto-dpif - fragment handling - actions

==21214== Conditional jump or move depends on uninitialised value(s)
==21214==    at 0x4B77C1: odp_flow_key_from_flow__ (odp-util.c:6143)
==21214==    by 0x46DB58: dp_netdev_upcall (dpif-netdev.c:6239)
==21214==    by 0x4774A7: handle_packet_upcall (dpif-netdev.c:6608)
==21214==    by 0x4774A7: fast_path_processing (dpif-netdev.c:6726)
==21214==    by 0x47933C: dp_netdev_input__ (dpif-netdev.c:6814)
==21214==    by 0x479AB8: dp_netdev_input (dpif-netdev.c:6852)
==21214==    by 0x479AB8: dp_netdev_process_rxq_port (dpif-netdev.c:4287)
==21214==    by 0x47A6A9: dpif_netdev_run (dpif-netdev.c:5264)
==21214==    by 0x4324E7: type_run (ofproto-dpif.c:342)
==21214==    by 0x41C5FE: ofproto_type_run (ofproto.c:1734)
==21214==    by 0x40BAAC: bridge_run__ (bridge.c:2965)
==21214==    by 0x410CF3: bridge_run (bridge.c:3029)
==21214==    by 0x407614: main (ovs-vswitchd.c:127)
==21214==  Uninitialised value was created by a stack allocation
==21214==    at 0x4769C3: fast_path_processing (dpif-netdev.c:6672)

'match' is allocated on stack but its 'wc' is accessed in
odp_flow_key_from_flow__ without proper initialization.
This patch fixes it.

Acked-by: William Tu <u9012063@gmail.com>
Signed-off-by: Yifeng Sun <pkusunyifeng@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

lib/dpif-netdev.c

@@ -6600,6 +6600,7 @@ handle_packet_upcall(struct dp_netdev_pmd_thread *pmd,
 
     match.tun_md.valid = false;
     miniflow_expand(&key->mf, &match.flow);
+    memset(&match.wc, 0, sizeof match.wc);
 
     ofpbuf_clear(actions);
     ofpbuf_clear(put_actions);