Failed to create_datagram_endpoint() with AF_UNIX family

• uvloop version: 0.15.2
• Python version: 3.7.3
• Platform: Debian GNU/Linux 10
• Can you reproduce the bug with PYTHONASYNCIODEBUG in env?:
• Does uvloop behave differently from vanilla asyncio? How?: asyncio correctly creates datagram unix socket

Code, works correctly using default event loop:

res = await loop.create_datagram_endpoint(MyProto, local_addr='/tmp/my_unix_sock', family=socket.AF_UNIX)

Trace:

Traceback (most recent call last):
  File "/usr/lib/python3.7/asyncio/runners.py", line 43, in run
    return loop.run_until_complete(main)
  File "uvloop/loop.pyx", line 1494, in uvloop.loop.Loop.run_until_complete
  File "./my_app.py", line 75, in main
    family = socket.AF_UNIX)
  File "uvloop/loop.pyx", line 3023, in create_datagram_endpoint
TypeError: local_addr must be a tuple of (host, port)

Start at uvloop/loop.pyx in create_datagram_endpoint around the reported line and run the supplied AF_UNIX reproducer, comparing its behavior with vanilla asyncio. Done means a datagram UNIX socket can be created with the shown local_addr and AF_UNIX family without breaking existing tuple-based endpoints.