repeater: clear buffer after ping

[Spaqin]

ARTIQ Pull Request

Description of Changes

Bugfix for repeaters for ARTIQ-8+: with multiple AUX buffers there could be a chance that more than one EchoReply packet would be received. Then TSC sync could fail, as it would read a EchoReply packet first rather than TSCAck, so the receiving buffer is cleared before syncing TSC, like in runtime (master) firmware.

Needs to be backported to ARTIQ-8.

Type of Changes

	Type
✓	:bug: Bug fix

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Licensing

See copyright & licensing for more info. ARTIQ files that do not contain a license header are copyrighted by M-Labs Limited and are licensed under LGPLv3+.

[sbourdeauducq]

Merging this since it's indeed consistent with the master, but I don't actually understand how you could get two EchoReply.