doc: mention linuxcaps support in FAQ
ntp: reconnect client sockets

With separate client sockets, allow the initial connect() to fail (e.g.
when the network is not reachable yet) and try to connect later when
sending the packet.

Also, reconnect the socket when the local address has changed.
ntp: move debug message after sendmsg()

This should reduce the delay before sending the packet when debugging is
enabled.
ntp: shorten setsockopt error messages