BUG/MINOR: quic: fix fd leak on startup check quic-conn owned socket

BUG/MINOR: quic: fix fd leak on startup check quic-conn owned socket

A startup check is done for first QUIC listener to detect if quic-conn
owned socket is supported by the system. This is done by creating a
dummy socket reusing the listener address. This socket must be closed as
soon as the check is done.

The socket condition is invalid as it excludes zero which is a valid
file-descriptor value. Fix this bug by adjusting this condition.

In theory, this bug could prevent the usage of quic-conn owned socket as
startup check would report a false error. Also, the file-descriptor
would leak as it is not closed. In practice, this cannot happen when
startup check is done after a 'quic4/quic6' listener is instantiated as
file-descriptor are allocated in ascending order by the system.

This should fix github issue #1954.

quic-conn owned socket implementation is scheduled for backport on 2.7.
This commit must be backported with it, more specifically to fix the
following patch :
  75839a44e7e904bd1e332b58bd579e03b6d106f0
  MINOR: quic: startup detect for quic-conn owned socket support