Add Alltoallv RCCL kernel implementation (#269)

* Add alltoallv API and implementation

* Extend Rome P2P channel limit to multinode and alltoall kernels

* topo_expl: fix compilation and sync up with main

* gtest: use RCCL alltoallv API

* Code review changes

[ROCm/rccl commit: b871ea3c0c]

projects/rccl/tools/topo_expl/include/utils.h

@@ -26,6 +26,7 @@ struct allGather3Data_t{
   int fullCudaCompCap;
   int nChannels;
   int gcn;
+  int alltoallDisable;
   struct ncclGraphInfo tree;
   struct ncclGraphInfo ring;
   struct ncclGraphInfo collNet;