ENETUNREACH and ENETDOWN were not in the list of retriable errors on
non-Windows platforms, so a single failed connection aborted the
transfer instead of being retried as a low level retry. The Windows
list already includes the equivalent WSAENETUNREACH and WSAENETDOWN.
This is easy to hit on a host with IPv6 enabled but no IPv6 route: if
the A lookup fails transiently while the AAAA lookup succeeds, the only
address to dial is IPv6 and the connect fails with ENETUNREACH. A retry
resolves again and normally succeeds.
(cherry picked from commit 94e319d2fa)
nielash