Revert "Set port variable instead of placeholder"

This reverts commit 6b4d2fddbb5859c2ef0ebdcbf133b21006daeffc.

...because it didn't work. I just got an empty box and the variable wasn't set
Set placeholder text to "Port" instead so it is clear what is needed here
Merge pull request #343 from glowing-bear/defaultport

Fix default port