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/astlpc.c b/astlpc.c
index 7ab78d6..de3982c 100644
--- a/astlpc.c
+++ b/astlpc.c
@@ -356,7 +356,7 @@
 	astlpc->binding.version = 1;
 	astlpc->binding.tx = mctp_binding_astlpc_tx;
 	astlpc->binding.start = mctp_binding_astlpc_start;
-	astlpc->binding.pkt_size = MCTP_BMTU;
+	astlpc->binding.pkt_size = MCTP_PACKET_SIZE(MCTP_BTU);
 	astlpc->binding.pkt_pad = 0;
 	astlpc->lpc_map = NULL;