http: make timeout event work with agent timeout

[lpinca]

The 'timeout' event is currently not emitted on the ClientRequest
instance when the socket timeout expires if only the timeout option
of the agent is set. This happens because, under these circumstances,
listenSocketTimeout() is not called.

This commit fixes the issue by calling it also when only the agent
timeout option is set.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• commit message follows commit guidelines

[nodejs-github-bot]

@lpinca sadly an error occured when I tried to trigger a build :(

[lpinca]

CI: https://ci.nodejs.org/job/node-test-pull-request/20102/

[lpinca]

cc: @nodejs/http
New CI: https://ci.nodejs.org/job/node-test-pull-request/20222/ (:heavy_check_mark:)

[addaleax]

@lpinca Do you want to merge this?

[lpinca]

@addaleax let's wait a little more for another approval, it's not a critical issue. We can merge this in a couple of days if nothing changed.

Thank you.

[lpinca]

Landed in 4b6e4c1.

[targos]

The test added in this PR fails on my computer:

AssertionError [ERR_ASSERTION]: Expected "actual" to be reference-equal to "expected":
+ actual - expected ... Lines skipped

  Comparison {
+   code: 'EHOSTUNREACH',
+   message: 'connect EHOSTUNREACH 192.0.2.1:80',
-   code: 'ECONNRESET',
-   message: 'socket hang up',
    type: [Function: Error] {
...
    }
  }
    at new AssertionError (internal/assert.js:396:11)

[lpinca]

Ok, I will change it to prevent it from using a non routable IP address so it will not be flaky. I'll get to it as soon as I can.