net: http: Add timeout to HTTP server response

Allow the caller to delay the closing of the HTTP connection
for a number of milliseconds. The purpose for this is that
the client can send still some data back to us for a short
period of time.

This is needed for example for Basic authentication so that
server is able to receive authentication values back.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>