ofproto-dpif: Uninitialize 'xlate_cache' to free resources

Valgrind reported:

1210: ofproto-dpif - continuation after clone

==32205== 4,392 (1,440 direct, 2,952 indirect) bytes in 12 blocks are definitely lost in loss record 359 of 362
==32205==    at 0x4C2DB8F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==32205==    by 0x532574: xmalloc (util.c:138)
==32205==    by 0x4F98CA: ofpbuf_init (ofpbuf.c:123)
==32205==    by 0x42C07B: nxt_resume (ofproto-dpif.c:5110)
==32205==    by 0x41796F: handle_nxt_resume (ofproto.c:3677)
==32205==    by 0x424583: handle_single_part_openflow (ofproto.c:8473)
==32205==    by 0x424583: handle_openflow (ofproto.c:8606)
==32205==    by 0x4579E2: ofconn_run (connmgr.c:1318)
==32205==    by 0x4579E2: connmgr_run (connmgr.c:355)
==32205==    by 0x41E0F5: ofproto_run (ofproto.c:1845)
==32205==    by 0x40BA63: bridge_run__ (bridge.c:2971)
==32205==    by 0x410CF3: bridge_run (bridge.c:3029)
==32205==    by 0x407614: main (ovs-vswitchd.c:127)

This is because 'xcache' was not destroyed properly. 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>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

ofproto/ofproto-dpif.c

@@ -5095,6 +5095,7 @@ nxt_resume(struct ofproto *ofproto_,
     /* Clean up. */
     ofpbuf_uninit(&odp_actions);
     dp_packet_uninit(&packet);
+    xlate_cache_uninit(&xcache);
 
     return error;
 }