unix stack may raise in `listen`

[hannesm]

The Unix.bind in Tcpv4v6_socket is not guarded and may raise an exception. This leaks file descriptors, and the interface should be revised (or specified in a way that allows exceptions to occur).

Maybe a check in "connect" should be done if the IP address(es) are available at the moment (though obviously that may change during the operation of a unikernel.

Any ideas how to deal with that? Any networking unikernel were you specify dist/my-unikernel --ipv4=1.2.1.2/24 fails with an exeption (Unix.error EADDRNOTAVAIL) if 1.2.1.2 is not configured on the host.

[hannesm]

reported here from the issue comment robur-coop/tlstunnel#13 (comment)