Clients sockets are closed immediately after receiving valid response.
Don't wait for the first early HW TX timestamp to enable waiting for
late timestamps. It may take a long time or never come if the HW/driver
is consistently slow. It's a chicken and egg problem.
Instead, simply check if HW timestamping is enabled on at least one
interface. Responses from NTP sources on other interfaces will always be
saved (for 1 millisecond by default).
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