Limit P2P channels per peer to not exceeding max channels (#1594)

* Limit P2P channels per peer to not exceeding max channels

* [UT] test single GPU cases for all collectives

* [UT] fix out of range root value

[ROCm/rccl commit: 4237caad69]

projects/rccl/src/graph/paths.cc

@@ -908,6 +908,8 @@ ncclResult_t ncclTopoComputeP2pChannels(struct ncclComm* comm) {
     // Doubling P2P channels per peer on single node
     if (comm->topo->nodes[GPU].count == comm->topo->nRanks && (IsArchMatch(comm->topo->nodes[GPU].nodes[0].gpu.gcn, "gfx94") || IsArchMatch(comm->topo->nodes[GPU].nodes[0].gpu.gcn, "gfx950"))) comm->p2pnChannelsPerPeer *= 2;
     comm->p2pnChannels = std::min(pow2Up(comm->p2pnChannels), 4*CHANNEL_LIMIT);
+    // p2pnChannelsPerPeer cannot be greater than MAXCHANNELS
+    comm->p2pnChannelsPerPeer = std::min(comm->p2pnChannelsPerPeer, MAXCHANNELS);
   }
 
   // Init channels that weren't used so far