tests/vhost-user-bridge.c: Sanity check socket path length

tests/vhost-user-bridge.c: Sanity check socket path length

The vhost-user-bridge binary accepts a UNIX socket path on
the command line. Sanity check that this is short enough to
fit into a sockaddr_un before copying it in.

Fixes: Coverity CID 1432866
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20210901152632.25511-1-peter.maydell@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>