stats: Add stat_item for value monitoring
This commit adds instrumentation function to gather measurement
and statistical values similar to counter groups.
Multiple values can be stored per item, which can be retrieved in
FIFO order. Getting values from the item does not modify its state to
allow for multiple independant backends (e.g. VTY and statd).
When a new value is set, the oldest value gets silently overwritten.
Lost values are skipped when getting values from the item.
Sponsored-by: On-Waves ehf
9 files changed