Fix for embassy net dns entries not being extensible

[korken89]

Not sure if this is a good fix perse, but it allows for extending DNS setting in smoltcp up to 8 entries.
If this is not done these interfaces are hard linked to whatever the return of smoltcp is.

Other ways to achieve this is welcome. :)

[lulf]

How about pub async fn query<const N: usize>(...) -> Result<Vec<IpAddress, N>>?

This also reminds me that heapless is here used in a public API, which we should try to avoid, but one thing at a time perhaps :)

[korken89]

Hi @lulf

I tried that first but you get this error then:

error[E0308]: mismatched types
   --> src/lib.rs:592:9
    |
592 |         res
    |         ^^^ expected `N`, found `1`
    |
    = note: expected enum `Result<Vec<_, N>, dns::Error>`
               found enum `Result<Vec<_, 1>, _>`

For more information about this error, try `rustc --explain E0308`.

As this only can infer the N from external code, not internal that we get from smoltcp.

[nilfit]

With smoltcp-rs/smoltcp#855, we can use smoltcp::config::DNS_MAX_RESULT_COUNT for the size instead of choosing a new hard-coded size. Then dependent crates can freely choose which smoltcp/dns-max-result-count-* to use.

[lulf]

Thanks for the fix 🚀