Update af_unix.c to increase default max_dgram_qlen

[sbesse-nam]

updated max_dgram_qlen, the default of 10 caused problems in BusyBox init system. This may be better to be in a Kconfig somewhere, but unsure where as this default is currently not configurable.

[alexandrebelloni]

Can't you simply change the value in /proc/sys/net/unix/max_dgram_qlen?

[sbesse-nam]

I changed the value before creating a socket and observed the same issue (failed sending with -EAGAIN). It doesn't seem to immediately propagate and may need to be done at some earlier point in the boot process (before normal applications are running perhaps). Regardless of it is possible to actually change it during runtime, the default value of 10 is very small. As far as I understand, changing this value doesn't change the memory allocated to the socket, so I don't see a reason why the default shouldn't be a higher value.