Signed-off-by: Yang Qian <yang.qian@citrix.com>

1. all types deriving from rpcty
2. remove redundent rpc functions, replace them with `@@default` rewriter
3. rename `Basic` of `string_of_port_kind` to `Basic_port`
4. change type `ipv4_route_t` from list to a struct type
5. move exception definition to xcp-networkd
6. declare interface with new style code by using `Idl.declare`
7. replace optional parameter with position parameter or position option
parameter, remove the redundent suffix unit parameter accordingly
8. replace `rpc_of_x` and `x_of_rpc` with `Rpcmarshal.marshal` and `Rpamarshal.unmarshal`
9. update jbuilder file, remove redundant contents

Signed-off-by: Yang Qian <yang.qian@citrix.com>

Signed-off-by: Yang Qian <yang.qian@citrix.com>