#1325 Add option to disable caching for large number of interfaces

[Sam Tannous]

At high scale (large number of interfaces (over 2000)) there is considerable churn (high CPU) as the ifTable and ip MIBs loop through all the interfaces and routes every 15/5 seconds (respectively). This patch adds a commandline option -y to disable this caching. Disabling the caching makes some ifTable attributes inaccurate (e.g. IF-MIB::ifLastChange).

This was tested against latest V5-7-patches on Debian Jessie on an amd64 platform.

Thanks,
Sam Tannous (stannous@cumulusnetworks.com)
Cumulus Networks