rtnl: removes non_exhaustive from NextHop structs. fixes #25

[cjmakes]

Having these structs marked as non_exhaustive makes it impossible to construct a NextHop object. Constructing this object is useful for creating MultiPath routes which have multiple hops.

fixes #25

[cathay4t]

Unlike NetlinkHeader, the kernel team might add new property to this struct, when it happens without non_exhaustive , this crate are forced to bump version from 1.x to 2.x which not acceptable for crate consumer.

If you have proof showing kernel will never change this struct, please state.

For constructing this object in your code, we can introduce Default treat or fn new() or From<> for this struct.

I am currently refactoring the code of route component, will take this into consideration.

[cathay4t]

Without looking to kernel code deeply, I cannot tell the correct way of doing this. Stay tune for my conclusion on kernel code study.

[cathay4t]

The content of NextHop is a group of netlink attributes, we should never expose it as NextHopBuffer. Will fix it in the coming refactor.

[cathay4t]

@cjmakes I have create PR #64 which you can use RouteNextHop::default() to generate NextHop. It is not a single fixed size buffer, but could contains a list of netlink attributes.

[cathay4t]

The new release 0.18.1 has proper way to initialize a RouteNextHop

Closing. Feel free to reopen if you think further work required.