Updates to libpldm base

Use constants to track pldm version and update some doxygen comments

Change-Id: I40ce1d606eb68b979fac825a3ddfaaa840e10810
Signed-off-by: Christian Geddes <crgeddes@us.ibm.com>
diff --git a/libpldm/base.c b/libpldm/base.c
index 6d9a67f..79f5ba5 100644
--- a/libpldm/base.c
+++ b/libpldm/base.c
@@ -34,7 +34,7 @@
 	msg->datagram = datagram;
 	msg->reserved = 0;
 	msg->instance_id = hdr->instance;
-	msg->header_ver = 0;
+	msg->header_ver = PLDM_CURRENT_VERSION;
 	msg->type = hdr->pldm_type;
 	msg->command = hdr->command;