core: help the compiler disambiguate

[wngr]

when pulling in libp2p as a dependency and compiling for wasm32-unknown-unknown, I hit this error:

    Checking libp2p-core v0.30.0-rc.1 (https://github.com/wngr/rust-libp2p?branch=wasm-support#19e47553)
error[E0283]: type annotations needed
  --> /home/ow/.cargo/git/checkouts/rust-libp2p-8eaa3598de58093a/19e4755/core/src/connection/pool/concurrent_dial.rs:84:28
   |
84 |             if dials.len() == concurrency_factor.get().into() {
   |                            ^^ ------------------------------- this method call resolves to `T`
   |                            |
   |                            cannot infer type
   |
   = note: cannot satisfy `usize: PartialEq<_>`

Not sure why this target dependant, and doesn't happen when running cargo check inside rust-libp2p though 😕

[mxinden]

Thanks for providing the patch right away @wngr! I will include this in the next v0.40.0 release candidate given it is a bug fix.