Implement SPCI_RX_RELEASE to replace hf_mailbox_clear.

Bug: 132421502
Change-Id: I63ffcce9b998ef98ff7ec3cdef41415a56a91b9f
diff --git a/test/linux/hftest_socket.c b/test/linux/hftest_socket.c
index 460d1f1..2e89d2b 100644
--- a/test/linux/hftest_socket.c
+++ b/test/linux/hftest_socket.c
@@ -68,7 +68,7 @@
 	/* Set up the mailbox. */
 	hf_vm_configure(send_addr, recv_addr);
 
-	hf_mailbox_clear();
+	spci_rx_release();
 
 	/* Clean the context. */
 	ctx = hftest_get_context();
@@ -98,7 +98,7 @@
 		spci_vm_id_t dst_id = spci_msg_send_sender(ret);
 		spci_vm_id_t src_id = spci_msg_send_receiver(ret);
 
-		hf_mailbox_clear();
+		spci_rx_release();
 		EXPECT_EQ(spci_msg_send(src_id, dst_id, spci_msg_send_size(ret),
 					0)
 				  .func,