* refactor out the bindmulti check into a function
* Correct a couple of checks against the inp - I was checking against
  the lookup result (t) instead of against the inp we are binding
  (inp).

Verified:

* bindmulti - correctly allows same-port binding
* reuseport - allows same-port binding
* bindmulti + reuseport - allows same-port binding
* none - doesn't allow same-port binding