Prevent spoofing of iq replies by verifying that the 'from' address
matches the 'to' address of the iq request.

This full extent of this problem was realized by Thijs Alkemade, while
investigating a problem reported to us by Fabian Yamaguchi and Christian
Wressnegger of the University of Goettingen)

This change was created by Thijs Alkemade, with small shuffling and
variable renaming by me.