test: adds outbound eviction functional tests, updates comment in ConsiderEviction

[sr-gi]

Motivation

While checking the outbound eviction code I realized a case was not considered within the comments, which in turn made me realize we had no functional tests for the outbound eviction case (when I went to check/add the test case).

This PR updates the aforementioned comment and adds functional tests to cover the outbound eviction logic, in addition to the existing unit tests found at src/test/denialofservice_tests.cpp.