Select sendrecv path based on collective data size (#391)

* Select sendrecv path based on collective data size

* Add comments on packing and unpacking group field

* Toggling RCCL_P2P_NET_DISABLE in combined calls unit tests

src/proxy.cc

@@ -287,7 +287,7 @@ ncclResult_t ncclProxySaveP2p(struct ncclComm* comm, struct ncclProxyArgs* args)
     sub->sendbytes = 0;
     sub->nsteps = DIVUP(sub->recvbytes, sub->recvChunkSize);
     if (sub->nsteps == 0) sub->nsteps = 1;
-    NCCLCHECK(SaveProxy(proxyRecv, peerrecv, args, NCCL_CONN_IDX_P2P));
+    NCCLCHECK(SaveProxy(proxyRecv, peerrecv, args, args->recvIdx));
   }
   if (sub->delta > 0 && sendbytesOrig >= ssize_t(0)) {
     int peersend = (comm->rank+sub->delta)%comm->nRanks;
@@ -295,7 +295,7 @@ ncclResult_t ncclProxySaveP2p(struct ncclComm* comm, struct ncclProxyArgs* args)
     sub->recvbytes = 0;
     sub->nsteps = DIVUP(sub->sendbytes, sub->sendChunkSize);
     if (sub->nsteps == 0) sub->nsteps = 1;
-    NCCLCHECK(SaveProxy(proxySend, peersend, args, NCCL_CONN_IDX_P2P));
+    NCCLCHECK(SaveProxy(proxySend, peersend, args, args->sendIdx));
   }
   // Reset proxy args for potentially multiple cuda graph launches
   // It is safe as long as SaveProxy copies contents of args to op