Convert sockstat collector to use ConstMetrics
Convert sockstat collector to use ConstMetrics

This suffers from the same concurrency bug as the netstat one:
https://github.com/prometheus/node_exporter/issues/280

derekmarcotte/node_exporter,siavashs/node_exporter,knweiss/node_exporter,ema/node_exporter,derekmarcotte/node_exporter,chosenken/node_exporter,chosenken/node_exporter,joehandzik/node_exporter,knweiss/node_exporter,joehandzik/node_exporter,prometheus/node_exporter,Jean-Daniel/node_exporter,Jean-Daniel/node_exporter,mslocrian/flexswitch_exporter,joehandzik/node_exporter,bs-github/node_exporter,chosenken/node_exporter,ema/node_exporter,bs-github/node_exporter,prometheus/node_exporter,chosenken/node_exporter,ema/node_exporter,knweiss/node_exporter,knweiss/node_exporter,cbstewart9393/node_exporter,siavashs/node_exporter,joehandzik/node_exporter,siavashs/node_exporter,Jean-Daniel/node_exporter,cbstewart9393/node_exporter,bs-github/node_exporter,ema/node_exporter,bs-github/node_exporter,derekmarcotte/node_exporter,siavashs/node_exporter,prometheus/node_exporter,Jean-Daniel/node_exporter,derekmarcotte/node_exporter,mslocrian/flexswitch_exporter