rtnetlink_server: Fix edge triggering

We need to receive messages until there are no more pending or else we
will leave messages in the file descriptor.

Change-Id: I3f4a5a7e57ccca62be76591d47c8317d995e527e
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/src/netlink.hpp b/src/netlink.hpp
index 754b4b4..be44d24 100644
--- a/src/netlink.hpp
+++ b/src/netlink.hpp
@@ -34,7 +34,7 @@
  *  @param[in] sock - The socket to receive the messages on
  *  @param[in] cb   - Called for each response message payload
  */
-void receive(int sock, ReceiveCallback cb);
+size_t receive(int sock, ReceiveCallback cb);
 
 /* @brief Call on an rtnetlink payload
  *        Updates the input to remove the attr parsed out.