net/chrony: Fix chrony running as server and using bindaddress

On FreeBSD, sendmsg() fails when IP_SENDSRCADDR specifies a source
address on a socket that is bound to the address. This prevents a server
configured with the bindaddress directive from responding to clients.

Add a new variable to check whether the server IPv4 socket is not bound
before setting the source address.

PR: 233644
Submitted by: Colin T <bugzilla@nulldir.e4ward.com>
Reported by: ddrinnon@cdor.net
Approved by: maintainer timeout (> 3 weeks)
Obtained from: https://git.tuxfamily.org/chrony/chrony.git/commit/?id=6af39d63aa9323b4b8c39efe24ae0c88c949a901