Some kinds of Layerscape PCIe controllers will forward the received message
TLPs to system application address space, which could corrupt system memory
or lead to a system hang.  Enable MSG_DROP to fix this issue.
Signed-off-by: NMinghuan Lian <Minghuan.Lian@nxp.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>