engine: don't iterate map with keyset in LinkHelper

Iterate map with entryset for more efficient iteration.
Solves findbug warning of type WMI_WRONG_MAP_ITERATOR

Change-Id: I62da8696f89f111b6a3872f02ec8a6dd1663fc34
Signed-off-by: Alissa Bonas <abonas@redhat.com>