sysctl: Adopt more settings from the IBM HPC guidelines

sysctl: Adopt more settings from the IBM HPC guidelines

https://www.ibm.com/developerworks/community/wikis/home?lang=en#!/wiki/Welcome%20to%20High%20Performance%20Computing%20%28HPC%29%20Central/page/Linux%20System%20Tuning%20Recommendations

Since we have already configured most of our IP/TCP stack
for low latency and fast throughput, these settings complete
those efforts.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>
Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>