Cherry pick gNMI and Stratum related changes to this branch

Cherry picked commits:
20211 Update gNMI version and build script
20247 [ONOS-7829] Implement AbstractGrpcClient and AbstractGrpcClientControl
20233 [ONOS-7141][ONOS-7142] Add GnmiClient and GnmiController
20234 Refactor OpenConfig gNMI device description descovery
20260 [ONOS-7831] Implement GnmiHandshaker
20270 Add Stratum driver

Change-Id: I81ad8bce45251af5909cfcac0edbcfd11c8ebf1d
diff --git a/WORKSPACE b/WORKSPACE
index f08f71b..9ccf9bf 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -54,6 +54,10 @@
 
 generate_p4lang()
 
+load("//tools/build/bazel:gnmi_workspace.bzl", "generate_gnmi")
+
+generate_gnmi()
+
 git_repository(
     name = "build_bazel_rules_nodejs",
     remote = "https://github.com/bazelbuild/rules_nodejs.git",