Add SystemMessages protos to Connectivity

This follows the model used for the same protos by the Wifi module in
service-wifi.

SystemMessageProto is used by NetworkNotificationManager to define IDs
for notifications that are also counted in system notification metrics.

Bug: 171860710
Test: m
Change-Id: Iec674913fad9ad59c04249714a08b5a0d8ab0f84
diff --git a/service/Android.bp b/service/Android.bp
index f630cea..1330e71 100644
--- a/service/Android.bp
+++ b/service/Android.bp
@@ -68,6 +68,7 @@
         "net-utils-framework-common",
         "netd-client",
         "PlatformProperties",
+        "service-connectivity-protos",
     ],
     apex_available: [
         "//apex_available:platform",
@@ -76,6 +77,21 @@
 }
 
 java_library {
+    name: "service-connectivity-protos",
+    proto: {
+        type: "nano",
+    },
+    srcs: [
+        ":system-messages-proto-src",
+    ],
+    libs: ["libprotobuf-java-nano"],
+    apex_available: [
+        "//apex_available:platform",
+        "com.android.tethering",
+    ],
+}
+
+java_library {
     name: "service-connectivity",
     installable: true,
     static_libs: [