ixgbe, xsk: Migrate to new MEM_TYPE_XSK_BUFF_POOL

Remove MEM_TYPE_ZERO_COPY in favor of the new MEM_TYPE_XSK_BUFF_POOL
APIs.

v1->v2: Fixed xdp_buff data_end update. (Björn)

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Cc: intel-wired-lan@lists.osuosl.org
Link: https://lore.kernel.org/bpf/20200520192103.355233-11-bjorn.topel@gmail.com