Use boost::asio::post() instead of io->post()

According to the documentation io->post is deprecated, saying
that boost::asio::post() should be used instead.

Tested: ipmid runs the same as it did before.

Change-Id: I552c7cb5cb8ad8f9f6e2bcffa61ce5135e2faad2
Signed-off-by: Vernon Mauery <vernon.mauery@linux.intel.com>
diff --git a/include/ipmid/api.hpp b/include/ipmid/api.hpp
index f4cbf13..6e33470 100644
--- a/include/ipmid/api.hpp
+++ b/include/ipmid/api.hpp
@@ -47,7 +47,7 @@
 template <typename WorkFn>
 static inline void post_work(WorkFn work)
 {
-    getIoContext()->post(std::forward<WorkFn>(work));
+    boost::asio::post(*getIoContext(), std::forward<WorkFn>(work));
 }
 
 enum class SignalResponse : int