Licensing clarifications in Linux source files:

Licensing clarifications in Linux source files:
 1. Make it clear in all dual-licensed files that the
    license when distributed with Linux is GPLv2.
 2. Add MODULE_LICENSE(dual) in a few places.
 3. Change many of our EXPORT_SYMBOL() decls to EXPORT_SYMBOL_GPL().
    This is the preference of the Linux maintainers, and avoids any
    trouble down the road if our EXPORT_SYMBOL'ed functions use Linux
    internal interfaces that are GPL only.

Signed-off-by: Keir Fraser <keir@xensource.com>