MAINTAINERS: xen: Konrad to step down and Juergen to pick up

I've lately been concentrating on other projects and haven't been
doing much of Xen core maintainership for the last year.

I am quite thrilled that Juergen is willing to help out!

P.S.
I am still the maintainer of Xen-SWIOTLB, Xen PCI-[front|backend],
and co-maintainer of Xen block-[front|backend]; amongst others.
Acked-by: NJuergen Gross <jgross@suse.com>
Acked-by: NBoris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: NDavid Vrabel <david.vrabel@citrix.com>

MAINTAINERS

@@ -12202,9 +12202,9 @@ S:	Maintained
 F:	drivers/media/tuners/tuner-xc2028.*
 
 XEN HYPERVISOR INTERFACE
-M:	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
 M:	Boris Ostrovsky <boris.ostrovsky@oracle.com>
 M:	David Vrabel <david.vrabel@citrix.com>
+M:	Juergen Gross <jgross@suse.com>
 L:	xen-devel@lists.xenproject.org (moderated for non-subscribers)
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip.git
 S:	Supported