pw_rpc: Use pw_function callbacks in RPC client

This updates the nanopb RPC client to use pw::Function for callbacks
instead of custom virtual interfaces.

Change-Id: I7c548cde00223ec32e45cc831fe7f9f79577842b
Requires: pigweed-internal:13201
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/48484
Reviewed-by: Wyatt Hepler <hepler@google.com>
diff --git a/pw_protobuf_compiler/proto.cmake b/pw_protobuf_compiler/proto.cmake
index 911ba3a..62f6eaf 100644
--- a/pw_protobuf_compiler/proto.cmake
+++ b/pw_protobuf_compiler/proto.cmake
@@ -299,6 +299,7 @@
   target_link_libraries("${NAME}.nanopb_rpc"
     INTERFACE
       "${NAME}.nanopb"
+      pw_rpc.nanopb.client
       pw_rpc.nanopb.method_union
       pw_rpc.server
       ${DEPS}