libmctp: Clarify BTU-related symbols

DSP0236 defines a Baseline Transmission Unit (BTU), which dictates the
minimum supported packet payload size. The packet size is the BTU + the
packet header. The maximum (payload) transport unit size for a given
binding may be larger than the BTU.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: I2c4013531efd572d95c5a61e4d59309490505a8f
diff --git a/tests/test_bridge.c b/tests/test_bridge.c
index 496ae19..43b5d76 100644
--- a/tests/test_bridge.c
+++ b/tests/test_bridge.c
@@ -68,7 +68,7 @@
 	binding->binding.name = "test";
 	binding->binding.version = 1;
 	binding->binding.tx = mctp_binding_bridge_tx;
-	binding->binding.pkt_size = MCTP_BMTU;
+	binding->binding.pkt_size = MCTP_PACKET_SIZE(MCTP_BTU);
 	binding->binding.pkt_pad = 0;
 	return binding;
 }