maintainers: claim responsability for Xen
maintainers: claim responsability for Xen

As some users are still using xen as the hypervisor, I suggest to
continue support for xen in DPDK. And from 16.11, I will be the
maintainer of all xen-related files.

Signed-off-by: Jianfeng Tan <4339d9ba3a87a0d192e405945005ff86667f7b0c@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk