[roll third_party/pigweed] 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.

Original-Requires: pigweed-internal:13201
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/48484

third_party/pigweed Rolled-Commits: ecbdb697920d57a..bebba90c0161c81
Roller-URL: https://ci.chromium.org/b/8844704986879161441
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8844704986879161441
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I2dd95755c8a3a2b6cd76b4adbe5f4dca890f001a
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/48660
Reviewed-by: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index ecbdb69..bebba90 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit ecbdb697920d57a8eddb913d331d027335f93de3
+Subproject commit bebba90c0161c8185a4f5dba4b1aabe3ff635e66