@2429793 Bump version to 1.6.1

@2428602 Update all *intf_mgr documentation for exists, on_*intf_crea…

…te, and on_*intf_delete

@2352705 Introduce a new API to increase an agent's attrlog buf size.

@2313258 Add agent status accessors and agent iterators for options/s…

…tatus.

@2285936 Add missing stub handler for eth_lag_intf_handler

@2285705 Add the missing stub definition for eth_lag_intf_member_iter

@2206485 Add BSD 3-clause license

@2205052 Add a README.md to take precedence on the GitHub site

@2200282 Add @file tag to intf.h to avoid doxygen getting confused

@2135195 Update decap group comment verbiage