If two or more rapid dns requests for the same server are done
from different threads it turns into separate dns reques, if
the response of the request isn't found in the cache.
This patch avoid multiple request for the same server by
letting subsequents request wait until the first request
has finished.
Change-Id: Ic72ea0e7d3964a4164eddf866feb4357ec4dfe54
Initial commit for dns cache per interface.
Added a type that holds a reference to a
cache and name of associated interface,
address of interface, name server(s)
associated with an interface etc.
New functions to set default interface,
address of name servers etc.
Change-Id: Ie991bc5592fd998409853d8bf77d7fe69035dac5
