Don't stop online burst for unreachable sources until sending succeeds.
This is mainly useful with iburst when chronyd is started before the
network is configured.
Switch to NTP for presend as the echo service (RFC 862) is rarely
enabled. When presend is active, send an NTP client packet to the
server/peer and ignore the reply.
This also fixes presend with separate client sockets. The destination
port can't be changed on connected sockets, so the echo packet was sent
to the NTP port instead of the echo port.
NTP timestamps use only 32 bits to count seconds and the current NTP era
ends in 2036. Add support for converting NTP timestamps from other NTP
eras on systems with 64-bit time_t.
The earliest assumed NTP time is set by the configure script (by default
to 50 years before the date of the build) and earlier NTP timestamps
underflow to the following NTP era.
Create a new connected client socket before each request and close it
when a valid reply is received.
This is useful when the network configuration is changed and the client
socket should be reconnected, but the old bound address remains valid
and sendmsg() doesn't return with an error.
This will be needed to prevent loading of dump files after sources have
already accumulated samples and possibly reference was already updated
when async resolving of sources is implemented.
When source is set as active, it's receiving reachability updates (e.g.
offline NTP sources are not active).
Also add function to count active sources.
Explicitly set the number of iburst samples to the size of the register
to make sure there are at least 7 reachability updates and the
initstepslew mode can be ended.
If acquisitionport is set to 0 (default), create and connect a new
socket for each server instead of using one socket per address family
for all servers.
If the remote stratum is higher than ours, try to lock on the peer's
polling to minimize our response time by slightly extending our delay or
waiting for the peer to catch up with us as the random part in the
actual interval is reduced. If the remote stratum is equal to ours, try
to interleave evenly with the peer.
If the remote peer uses a polling interval shorter than the local
minimum, the local peer will be unable to send any packets as the
timeout will be updated on every received valid packet and will never
expire.
Modify the delay calculation to aim at poll interval away since the last
transmit.
Also, share the delay calculation code with transmit_timeout().
