proto: Split reusable structures into their own package

Some structures such as Interface and Route are not only used by the
kata-agent since they are generic enough to be reused by kata-runtime
or kata-netmon.

By splitting those structures into their separate package, we prevent
their consumers from importing the whole protocols/grpc package which
pulls a lot of unneeded content.

Fixes kata-containers#399

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

hack/update-generated-agent-proto.sh

@@ -3,7 +3,14 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 #
-protoc -I=$GOPATH/src -I=$GOPATH/src/github.com/gogo/protobuf/protobuf \
+
+protoc \
+	pkg/types/types.proto --gogofast_out=.
+
+protoc \
+	-I=$GOPATH/src \
+	-I=$GOPATH/src/github.com/gogo/protobuf/protobuf \
+	-I=pkg/types \
 	--proto_path=protocols/grpc --gogofast_out=\
 Mgoogle/protobuf/any.proto=github.com/gogo/protobuf/types,\
 Mgoogle/protobuf/duration.proto=github.com/gogo/protobuf/types,\
@@ -12,4 +19,4 @@ Mgoogle/protobuf/timestamp.proto=github.com/gogo/protobuf/types,\
 Mgoogle/protobuf/wrappers.proto=github.com/gogo/protobuf/types,\
 Mgoogle/protobuf/empty.proto=github.com/gogo/protobuf/types,\
 plugins=grpc:protocols/grpc \
-	protocols/grpc/*.proto
+	protocols/grpc/*.proto \