[fgnhgorch] Changes for Fine Grained ECMP (#1315)

* Fine grained ECMP initial commit
* Fix compilation, test failures and add logic to query SAI_NEXT_HOP_GROUP_ATTR_REAL_SIZE from SAI
* Misc fixes after migrating branch
* Misc-fixes
* Add support to fgnhgorch for neighbor and interface availability changes
* fgnhg group/prefix/member addition and deletion
* fix indentation and address comment
* Improve error handling and add support for crm and neigh refcounts
* Temporarily disable dynamic changes to route from fine grained to standard ecmp
* Add checks to limit Fine Grained ECMP to default VRF
* handle fgnhg prefix addition deletion with route bulker
* fix indentation
* Add handling for neigh edge case scenarios and improve routeorch bulker integration
* write route entry to state_db
* Fix bug with add and remove nh in a bank at the same time
* Improve test coverage and fix issues with multi-nh changes, misc code improvements
* Improve distribution of hash buckets per nh when hash buckets are not divisible by # of buckets
* Incorporate review comments v1
* Reduce exposure of private routeorch functions/variables outside of routeorch
* Fix an uninitialized variable error found in testing
* Change test_fgnhg.py to use the new framework to validate db entries
* Remove exposure of routeorch nextHopGroupCounts outside of routeorch, and misc. improvements
* camelCase changes for fgnhgorch
* RouteOrch add/removeRoutePost do not need logic to reroute calls to fgnhgorch
* camelCase changes v2

Author: anish-n

orchagent/Makefile.am

@@ -35,6 +35,7 @@ orchagent_SOURCES = \
             neighorch.cpp \
             intfsorch.cpp \
             portsorch.cpp \
+            fgnhgorch.cpp \
             copporch.cpp \
             tunneldecaporch.cpp \
             qosorch.cpp \