Allow empty values for ingress and egress qdisc limits

If the user does not specify the limit values the system will fill in its own reasonable defaults
Implement get_limit in functions.sh

get_limit will allow reasonable default values for qdiscs if the user
left the GUI fields empty. On a small memory device like cerowrt home wndr3[7|8]00
fq_codels default of 10240 packets is too much, so clamp this down to 1000.
This implementation also tries to do the right thing for bfifo (needs more testing)
Merge branch 'master' of github.com:dtaht/ceropackages-3.3
Switch simple.qos and simplest.qos to use the get_limit function

Change the qdisc scripts to use the get_limit functoin to set the actual limits.
This allows to specify no limit at all to use a qdiscs default limit.