Move to boost::asio::post

This allows entity_manager to compile with BOOST_ASIO_NO_DEPRECATED set.
It was functionally changed a few years ago, and is identical to the
other behavior.

Change-Id: I73b9bdeb9a079f843122c0bba545f2a08f965b68
Signed-off-by: Ed Tanous <edtanous@google.com>
diff --git a/sd_event_loop.cpp b/sd_event_loop.cpp
index c4fb762..df985c4 100644
--- a/sd_event_loop.cpp
+++ b/sd_event_loop.cpp
@@ -41,7 +41,8 @@
                           [this](const boost::system::error_code& ec) {
                               if (!ec)
                               {
-                                  io->post([this]() { startRmcpReceive(); });
+                                  boost::asio::post(
+                                      *io, [this]() { startRmcpReceive(); });
                                   handleRmcpPacket();
                               }
                           });