Update onos-gen-p4-constant script for new P4Runtime version

Change-Id: I6db9b826e743da70945903cdd934f47f18ba5a7b
diff --git a/tools/dev/bin/onos-gen-p4-constants b/tools/dev/bin/onos-gen-p4-constants
index 8e68acc..566ba4f 100755
--- a/tools/dev/bin/onos-gen-p4-constants
+++ b/tools/dev/bin/onos-gen-p4-constants
@@ -3,7 +3,7 @@
 import argparse
 import re
 import google.protobuf.text_format as tf
-from p4.config import p4info_pb2
+from p4.config.v1 import p4info_pb2
 
 
 copyright = '''/*