Prevent Internal Server Error if range is backwards
Prevent Internal Server Error if range is backwards

Fixes redmine #3950 - ip_range_to_subnet_array can easily swap the input parameters if the caller has passed/entered them the wrong way around. That is both friendly to the caller and ensures that a hostile caller can't blow up the routine.
This patch is for master (2.2)
jxmx/pfsense,ch1c4um/pfsense,pfsense/pfsense,ch1c4um/pfsense,NewEraCracker/pfsense,NewEraCracker/pfsense,BlackstarGroup/pfsense,ch1c4um/pfsense,BlackstarGroup/pfsense,NOYB/pfsense,NOYB/pfsense,pfsense/pfsense,phil-davis/pfsense,phil-davis/pfsense,dennypage/pfsense,dennypage/pfsense,BlackstarGroup/pfsense,ptorsten/pfsense,NOYB/pfsense,ptorsten/pfsense,dennypage/pfsense,brunostein/pfsense,NewEraCracker/pfsense,phil-davis/pfsense,NewEraCracker/pfsense,jxmx/pfsense,brunostein/pfsense,BlackstarGroup/pfsense,ch1c4um/pfsense,pfsense/pfsense,ptorsten/pfsense,pfsense/pfsense,jxmx/pfsense,dennypage/pfsense,brunostein/pfsense,phil-davis/pfsense