[flow][protobuf] set protobuf file syntax to version 2
[flow][protobuf] set protobuf file syntax to version 2

Specify the major syntax version of the protobuf file to version 2, to
avoid parsing warning with protobuf3 compiler.

safchain/skydive,skydive-project/skydive,skydive-project/skydive,lebauce/skydive,lebauce/skydive,lebauce/skydive,skydive-project/skydive,fdebonneval/skydive,safchain/skydive,lebauce/skydive,lebauce/skydive,safchain/skydive,lebauce/skydive,skydive-project/skydive,lebauce/skydive,safchain/skydive,skydive-project/skydive,fdebonneval/skydive,skydive-project/skydive,fdebonneval/skydive,safchain/skydive,safchain/skydive,redhat-cip/skydive,redhat-cip/skydive,safchain/skydive,skydive-project/skydive,redhat-cip/skydive,safchain/skydive,lebauce/skydive