Re-split the merge of the reorder-hostkeys test.

Re-split the merge of the reorder-hostkeys test.

In the kex_proposal_populate_entries change I merged the the check for
reordering hostkeys with the actual reordering, but kex_assemble_names
mutates options.hostkeyalgorithms which renders the check ineffective.
Put the check back where it was.  Spotted and tested by jsg@, ok djm@