chore: fix clippy warnings

[Darksonn]

This fixes the following clippy warnings. (They don't appear in CI because CI uses an older clippy.)

warning: this expression borrows a value the compiler would automatically borrow
  --> tokio/src/future/poll_fn.rs:38:9
   |
38 |         (&mut self.f)(cx)
   |         ^^^^^^^^^^^^^ help: change this to: `self.f`
   |
   = note: `#[warn(clippy::needless_borrow)]` on by default
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow

warning: methods called `is_*` usually take `self` by reference or no `self`
  --> tokio/src/io/util/vec_with_initialized.rs:67:28
   |
67 |     pub(crate) fn is_empty(&mut self) -> bool {
   |                            ^^^^^^^^^
   |
   = note: `#[warn(clippy::wrong_self_convention)]` on by default
   = help: consider choosing a less ambiguous name
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#wrong_self_convention

warning: unnecessary use of `to_vec`
   --> tokio/src/net/addr.rs:148:20
    |
148 |         let iter = self.to_vec().into_iter();
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^ help: use: `self.iter().copied()`
    |
    = note: `#[warn(clippy::unnecessary_to_owned)]` on by default
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_to_owned

[hawkw]

looks good to me!