selftests/bpf: Enable CONFIG_VSOCKETS in config

CONFIG_VSOCKETS is required by BPF selftests, otherwise we get errors
like this:

./test_progs:socket_loopback_reuseport:386: socket:
Address family not supported by protocol
socket_loopback_reuseport:FAIL:386
./test_progs:vsock_unix_redir_connectible:1496:
vsock_socketpair_connectible() failed
vsock_unix_redir_connectible:FAIL:1496

So this patch enables it in tools/testing/selftests/bpf/config.

Signed-off-by: Geliang Tang <[e-mail]>
Link: https://lore.kernel.org/r/472e[e-mail]
Signed-off-by: Martin KaFai Lau <[e-mail]>

tools/testing/selftests/bpf/config

···
 CONFIG_VXLAN=y
 CONFIG_XDP_SOCKETS=y
 CONFIG_XFRM_INTERFACE=y
+CONFIG_VSOCKETS=y