Decode APIs now accept const struct pldm_msg *msg

All the decode_xxx APIs were changed to accept the complete pldm_msg
instead of working with just a specific member (payload) making it
consistent with the encode_xxx APIs.

Following changes were made through out the code,
 - decode_xxx now requires to send the const struct pldm_msg *msg
   instead of a const uint8_t *msg.
 - Within the decode_xxx function the payload is extracted and used
   accordingly.
 - All the calls made to decode_xxx APIs have been modified to now
   pass the pointer to pldm_msg_hdr (struct pldm_msg *msg).
 - The test code was modified to now pass the appropriate data
   to all the encode_xxx APIs.

Change-Id: I16a3f6e554ea2c9fa44d55dc8f21f65022bd983a
Signed-off-by: Zahed Hossain <zahzahed@in.ibm.com>
diff --git a/libpldm/platform.c b/libpldm/platform.c
index d0929d9..f9c8351 100644
--- a/libpldm/platform.c
+++ b/libpldm/platform.c
@@ -55,7 +55,7 @@
 	return PLDM_SUCCESS;
 }
 
-int decode_set_state_effecter_states_resp(const uint8_t *msg,
+int decode_set_state_effecter_states_resp(const struct pldm_msg *msg,
 					  size_t payload_length,
 					  uint8_t *completion_code)
 {
@@ -67,12 +67,12 @@
 		return PLDM_ERROR_INVALID_LENGTH;
 	}
 
-	*completion_code = msg[0];
+	*completion_code = msg->payload[0];
 
 	return PLDM_SUCCESS;
 }
 
-int decode_set_state_effecter_states_req(const uint8_t *msg,
+int decode_set_state_effecter_states_req(const struct pldm_msg *msg,
 					 size_t payload_length,
 					 uint16_t *effecter_id,
 					 uint8_t *comp_effecter_count,
@@ -88,7 +88,7 @@
 	}
 
 	struct pldm_set_state_effecter_states_req *request =
-	    (struct pldm_set_state_effecter_states_req *)msg;
+	    (struct pldm_set_state_effecter_states_req *)msg->payload;
 
 	*effecter_id = le16toh(request->effecter_id);
 	*comp_effecter_count = request->comp_effecter_count;