FreeBSD 11.4's soconnectat() (sys/kern/uipc_socket.c) disconnects a
connected socket of a protocol without PR_CONNREQUIRED before it calls
pru_connect. udp_disconnect() and udp6_disconnect() drop the peer and
reset the local address, then in_pcbconnect_setup() and in6_pcbladdr()
fail port 0 with EADDRNOTAVAIL, so the socket is left unconnected.
connect to port 0 on a connected datagram socket now dissolves the
association through the AF_UNSPEC disconnect path before failing with 49,
where it kept the old peer. Stream sockets keep EISCONN.