[Bug] Fix file opening mode for logging.

Change-Id: I61de4ae716efdeb17c36c0576642d6b187b0203a

rpc_tool/verify_rpc/rpc_tool.py

diff --git a/rpc_tool/verify_rpc/rpc_tool.py b/rpc_tool/verify_rpc/rpc_tool.py
index d053eb3..fc516e7 100644
--- a/rpc_tool/verify_rpc/rpc_tool.py
+++ b/rpc_tool/verify_rpc/rpc_tool.py
@@ -162,7 +162,7 @@
     @staticmethod
     def write_hdlc_log(data: bytes) -> None:
         """Stores HDLC RPC logs."""
-        with open(_PW_HDLC_LOG, "w") as output:
+        with open(_PW_HDLC_LOG, "a") as output:
             output.write(data.decode() + "\n")
             output.flush()