MINOR: connection: skip FD-based syscalls for FD-less connections

MINOR: connection: skip FD-based syscalls for FD-less connections

Some syscalls at the TCP level act directly on the FD. Some of them
are used by TCP actions like set-tos, set-mark, silent-drop, others
try to retrieve TCP info, get the source or destination address. These
ones must not be called with an invalid FD coming from an FD-less
connection, so let's add the relevant tests for this. It's worth
noting that all these ones already have fall back plans (do nothing,
error, or switch to alternate implementation).