selftests/xsk: Add a test for shared umem feature

selftests/xsk: Add a test for shared umem feature

Add a new test for testing shared umem feature. This is accomplished by
adding a new XDP program and using the multiple sockets.

The new XDP program redirects the packets based on the destination MAC
address.

Signed-off-by: Tushar Vyavahare <tushar.vyavahare@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
Link: https://lore.kernel.org/bpf/20230927135241.2287547-9-tushar.vyavahare@intel.com