[BLUETOOTH] l2cap: don't mangle cmd.len

Since nobody uses it after we convert it to host-endian,
no need to do that at all.  At that point l2cap is endian-clean.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: David S. Miller <davem@davemloft.net>