pool: Clean up local interface resolution in HTTP transfer service

I don't see a reason for the complicated fallback in the loop - it
appears that it would never be used. A similar change was recently
made in the xrootd transfer service.

Target: trunk
Require-book: no
Require-notes: no
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: http://rb.dcache.org/r/5452/