ipmid: Fix Get BT Interface Capabilities response

Per the IPMI 2.0 spec, the input and output buffer size
must be maximum buffer size minus one byte to allocate
space for the length byte.

Change-Id: Ie1768b9c6844275f7897fbf8056ce2a19b1c11c3
Fixes: openbmc/openbmc#847
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/apphandler.cpp b/apphandler.cpp
index 431cbf0..28d97c9 100644
--- a/apphandler.cpp
+++ b/apphandler.cpp
@@ -405,7 +405,9 @@
     // Status code.
     ipmi_ret_t rc = IPMI_CC_OK;
 
-    uint8_t str[] = {0x01, MAX_IPMI_BUFFER, MAX_IPMI_BUFFER, 0x0A, 0x01};
+    // Per IPMI 2.0 spec, the input and output buffer size must be the max
+    // buffer size minus one byte to allocate space for the length byte.
+    uint8_t str[] = {0x01, MAX_IPMI_BUFFER-1, MAX_IPMI_BUFFER-1, 0x0A, 0x01};
 
     // Data length
     *data_len = sizeof(str);