transport: Introduce a transport for testing purposes

I've put the test transport header along side the source file as its
presence and implementation is an internal detail to support the test
suite. No consumers of libpldm outside its test suite should have any
need for the test transport. We can always choose to make the header
public if for some reason someone does eventually want to use it.

In addition, add a new test suite exercising the transport interfaces.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: Ie9906bdc6a397436b91198196de04ffd6c93fc46
diff --git a/src/transport/meson.build b/src/transport/meson.build
index 511b1c4..b0ef1ca 100644
--- a/src/transport/meson.build
+++ b/src/transport/meson.build
@@ -2,5 +2,6 @@
   'af-mctp.c',
   'mctp-demux.c',
   'socket.c',
-  'transport.c'
+  'transport.c',
+  'test.c'
 )