Rework PW_RPC Android.bp file

Android.bp should declare the current SDK version otherwise the
"private" SDK is used which limits who can call it.

Also, add a target for the echo proto for use by those wanting to create
a demo.

Test: compile Android code
Change-Id: Icdae7cec8089c303b1a80df820b814e6e661b498
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/78040
Reviewed-by: Wyatt Hepler <hepler@google.com>
Commit-Queue: Anthony Stange <stange@google.com>
Pigweed-Auto-Submit: Anthony Stange <stange@google.com>
diff --git a/pw_rpc/Android.bp b/pw_rpc/Android.bp
index 2ddfd96..992d3ee 100644
--- a/pw_rpc/Android.bp
+++ b/pw_rpc/Android.bp
@@ -26,6 +26,7 @@
         "pw_rpc_packet_proto_java_lite",
     ],
     plugins: ["auto_value_plugin"],
+    sdk_version: "current",
 }
 
 java_library_static {
@@ -35,4 +36,16 @@
         type: "lite",
     },
     srcs: ["internal/packet.proto"],
+    sdk_version: "current",
 }
+
+java_library_static {
+    name: "pw_rpc_echo_proto_java_lite",
+    visibility: ["//visibility:public"],
+    host_supported: true,
+    proto: {
+        type: "lite",
+    },
+    srcs: ["echo.proto"],
+    sdk_version: "current",
+}
\ No newline at end of file
diff --git a/pw_rpc/echo.proto b/pw_rpc/echo.proto
index aacb6c0..f36ebbb 100644
--- a/pw_rpc/echo.proto
+++ b/pw_rpc/echo.proto
@@ -15,6 +15,8 @@
 
 package pw.rpc;
 
+option java_package = "dev.pigweed.pw_rpc.proto";
+
 service EchoService {
   rpc Echo(EchoMessage) returns (EchoMessage) {}
 }