shill: Adds test for multi-part netlink message handling.

BUG=chromium:224652
TEST=unittest

Change-Id: I7e7ae7e974fe69de67df7a5c84856a8f778fc077
Reviewed-on: https://gerrit.chromium.org/gerrit/56088
Commit-Queue: Wade Guthrie <wdg@chromium.org>
Reviewed-by: Wade Guthrie <wdg@chromium.org>
Tested-by: Wade Guthrie <wdg@chromium.org>
diff --git a/netlink_message.cc b/netlink_message.cc
index dfb75af..9d0ba3b 100644
--- a/netlink_message.cc
+++ b/netlink_message.cc
@@ -200,9 +200,7 @@
 const uint16_t DoneMessage::kMessageType = NLMSG_DONE;
 
 ByteString DoneMessage::Encode(uint32_t sequence_number) {
-  LOG(ERROR)
-      << "We're not supposed to send Done messages (are we?) to the kernel";
-  return ByteString();
+  return EncodeHeader(sequence_number);
 }
 
 void DoneMessage::Print(int header_log_level, int /*detail_log_level*/) const {