When kernel.h is used in the headers it adds a lot into dependency hell,
especially when there are circular dependencies are involved.

Replace kernel.h inclusion with the list of what is really being used.

While at it, move these includes below the include guard.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/18731e4f6430100d6500d6c4732ee028a729c085.1654325651.git.christophe.jaillet@wanadoo.frSigned-off-by: Paolo Abeni <pabeni@redhat.com>