svc: Add svc_xprt_names service to replace svc_sock_names

svc: Add svc_xprt_names service to replace svc_sock_names

Create a transport independent version of the svc_sock_names function.

The toclose capability of the svc_sock_names service can be implemented
using the svc_xprt_find and svc_xprt_close services.

Signed-off-by: Tom Tucker <[email protected]>
Acked-by: Neil Brown <[email protected]>
Reviewed-by: Chuck Lever <[email protected]>
Reviewed-by: Greg Banks <[email protected]>
Signed-off-by: J. Bruce Fields <[email protected]>