topo hiding: replace contact lumps with NOP
This prevents possible dangling pointers in the contact uri (changed by
the fix_nated_contact() function). Instead of deleting the lumps that
alter the contact, we replace them with a NOP and COND_FALSE.
(cherry picked from commit 4bba4d800cdb76c64c6a3b66b0849a0ff1eb90a2)