[roll third_party/pigweed] pw_rpc: Terminate-able socket client

Extends the integration test socket client so the RPC dispatch thread
can be cleanly shut down.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/92600

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: fa8e4c3dd5ff4cb..7339e260ae40f34
Roller-URL: https://ci.chromium.org/b/8814253201801789665
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8814253201801789665
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: If1e36bdd6ad66b34c8a71dd274d5d4f5009f7874
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/94547
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index fa8e4c3..7339e26 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit fa8e4c3dd5ff4cb818c46ccb6f059b337c0bc802
+Subproject commit 7339e260ae40f34d80e9e0519129adf4c4a32ae8