Fix various Clippy lints

[Thomasdezeeuw]

Also see #1776

[Darksonn]

Looks like you missed one.

error: read amount is not handled
  --> tests/close_on_drop.rs:62:23
   |
62 |                 match self.cli.read(&mut buf) {
   |                       ^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: use `Read::read_exact` instead, or handle partial reads
note: the result is consumed here, but the amount of I/O bytes remains unhandled
  --> tests/close_on_drop.rs:64:21
   |
64 |                     Ok(_) => panic!("the client socket should not be readable"),
   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unused_io_amount
   = note: `#[deny(clippy::unused_io_amount)]` on by default

[Thomasdezeeuw]

Looks like you missed one.

I probably missed a bunch because it doesn't trigger for me locally, only on the CI for some reason.

[Thomasdezeeuw]

I just love how it switches between some 1 error in the tests, then 1 error in the examples and back to the tests again...

[Darksonn]

My guess is the rustc version. Clippy lints can vary a lot.