Remote driver implementation of new migration API

Remote driver implementation of new migration API

* src/remote/remote_protocol.x: Define wire protocol for migration
  protocol v3
* daemon/remote.c: Server side dispatch
* src/remote/remote_driver.c: Client side serialization
* src/remote/remote_protocol.c, src/remote/remote_protocol.h,
  daemon/remote_dispatch_args.h, daemon/remote_dispatch_prototypes.h,
  daemon/remote_dispatch_ret.h, daemon/remote_dispatch_table.h:
  Re-generate files
* src/remote_protocol-structs: Declare new ABIs