pw_rpc: Add status to packet

This change adds a status field to the RPC packet proto and the Packet
class.

Change-Id: Ieec2e585219203dbe3a1d62ba650f5504bf4c7a5
diff --git a/pw_rpc/packet_test.cc b/pw_rpc/packet_test.cc
index 9dfe333..83d4ee8 100644
--- a/pw_rpc/packet_test.cc
+++ b/pw_rpc/packet_test.cc
@@ -30,6 +30,7 @@
   packet.set_service_id(0xdeadbeef);
   packet.set_method_id(0x03a82921);
   packet.set_payload(payload);
+  packet.set_status(Status::UNAVAILABLE);
 
   byte buffer[128];
   StatusWithSize sws = packet.Encode(buffer);
@@ -47,6 +48,7 @@
                         packet.payload().data(),
                         packet.payload().size()),
             0);
+  EXPECT_EQ(decoded.status(), Status::UNAVAILABLE);
 }
 
 }  // namespace