Instead of passing it by value, make sure to have one variable holding
the file descriptor. This should help Coverity stop complaining about a
resource leak.

The steps:

    9.  Condition vbp_write_proxy_v1(vt, s) != 0, taking true branch.
    10. leaked_handle: Handle variable s going out of scope leaks
        the handle.

If the return value is non-zero the socket is VTCP_close'd.

Refs #2244