[core] Fixed bonding packet timestamping

[maxsharabayko]

A more safe and straightforward fix of the issue with timestamping packets for bonding, compared to #1767.

The proposed fix

Use srctime for all member links, instead of using the srctime value set by the first member link which has successfully sent a packet.

The issue

The source time of a packet is stored as the number of microseconds since the SRT internal clock epoch.
However internal clock accuracy might be higher than 1 μs (e.g. 1 ns).
Therefore, the value returned in MSG_CTRL::src_time may have a lower accuracy compared to the actual time point used to timestamp a packet.
In the case of group sender, in particular, this may result in 1 μs timestamp difference of the same packet, sent over several links. The first link will use internal clock accuracy, while other links will have a μs accuracy of the src_time.

Example:

@485676736: pkt seqno %2131373032 ts=254960 (ts 00:58:28.139419815 [STD], start time 00:58:27.884459430 [STD])
@485676735: pkt seqno %2131373032 ts=254959 (ts 00:58:28.139419000 [STD], start time 00:58:27.884459430 [STD])