pw_router: Add module and static router implementation

This adds a pw_router module for routing packets over network links.
Initially, this module contains a basic StaticRouter which uses a static
routing table.

Change-Id: I5534c7fec5c622e7af6548c48793ff7f7d6dd098
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/29440
Commit-Queue: Alexei Frolov <frolv@google.com>
Reviewed-by: Ewout van Bekkum <ewout@google.com>
Reviewed-by: Keir Mierle <keir@google.com>
Reviewed-by: Wyatt Hepler <hepler@google.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index ff37967..20870ee 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -48,6 +48,7 @@
 add_subdirectory(pw_preprocessor EXCLUDE_FROM_ALL)
 add_subdirectory(pw_random EXCLUDE_FROM_ALL)
 add_subdirectory(pw_result EXCLUDE_FROM_ALL)
+add_subdirectory(pw_router EXCLUDE_FROM_ALL)
 add_subdirectory(pw_rpc EXCLUDE_FROM_ALL)
 add_subdirectory(pw_span EXCLUDE_FROM_ALL)
 add_subdirectory(pw_status EXCLUDE_FROM_ALL)