Remove the platform specificity, it is unnecessary complexity.
Deduplicate repeated code as a result of reduced complexity.
Split out error identification code.
Update call-sites and tests.
Updates #14551
Updates tailscale/corp#25648
Signed-off-by: James Tucker <james@tailscale.com>
Observed in the wild some macOS machines gain broken sockets coming out
of sleep (we observe "time jumped", followed by EPIPE on sendto). The
cause of this in the platform is unclear, but the fix is clear: always
rebind if the socket is broken. This can also be created artificially on
Linux via `ss -K`, and other conditions or software on a system could
also lead to the same outcomes.
Updates tailscale/corp#25648
Signed-off-by: James Tucker <james@tailscale.com>
