Don't assign HSDir flag to relay that can't handle BEGIN_DIR
Child ticket of legacy/trac#15801 (moved).
Because of legacy/trac#14202 (moved) (introduced in 0.2.6), directory authorities can assign the HSDir flag to a relay without a DirPort but relay can't handle
BEGIN_DIR cell if they don't have the DirPort set (see legacy/trac#15849 (moved)).
Commit 80bed1ac should be reverted and backported. Right now, we have 8 directory authorities that are >= 0.2.6 so we should backport this fix asap to 026.