Bluetooth: Fix endianness issue with L2CAP MPS configuration

Incoming configuration values must be converted to native CPU order
before use.  This fixes a bug where a little-endian MPS value is
compared to a native CPU value.  On big-endian processors, this
can cause ERTM and streaming mode segmentation to produce PDUs
that are larger than the remote stack is expecting, or that would
produce fragmented skbs that the current FCS code cannot handle.

Signed-off-by: Mat Martineau <mathewm@codeaurora.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>