Child ticket of legacy/trac#15801. Because of legacy/trac#14202 (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). Commit 80bed1ac96a3035f8c55ddced5528f0d7d16d386 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.