gallium/util: don't depend on implementation defined behavior in listen()

gallium/util: don't depend on implementation defined behavior in listen()

Using 0 as the backlog argument to listen() is exploiting implementation
defined behavior and will lead to no connections being accepted on some
libc implementations.

Quote of the listen manpage: "A backlog argument of 0 may allow the socket to
accept connections, in which case the length of the listen queue may be set to
an implementation-defined minimum value."

Fix this by using a more sensible backlog value.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>