Collect stats from /proc/net/snmp

This makes up part of the data of netstat statistics `netstat -s` besides /proc/net/netstat (which we already collect)
Remove empty line
Merge branch 'master' into net_snmp_stats
Set var for rate type
Get rid of metric variable, get rid of continue
Merge pull request #59 from StackExchange/net_snmp_stats

Net snmp stats