Fix memory leaks in cmdInterfaceEdit and cmdNWFilterEdit.

Fix memory leaks in cmdInterfaceEdit and cmdNWFilterEdit.

This applies a fix to thos functions similar to that made to cmdEdit
in 270895063d1cf86ab42fa220a8d090c24d58dbc0, thus fnixing a memory
leak - if tmp is unlinked and NULLed early in the function, the memory
used by tmp is never freed. Since we will always unlink tmp prior to
freeing its memory at the end of the function, just remove the earlier
code and let cleanup: do the cleanup.