Added RCCL env params to control setting the SO_REUSEADDR and SO_LINGER socket options (#1418)

* Added RCCL env params to control setting the SO_REUSEADDR and SO_LINGER socket options. This can allow control over the number of file descriptors created during bootstrapping.

* Casted the linger value to `int` sooner to avoid a scope of unknown typed-ness.

* Added CHANGELOG entry for this feature.

src/misc/socket.cc

@@ -15,6 +15,9 @@
 #include <sys/syscall.h>
 #include "param.h"
 
+RCCL_PARAM(SocketReuseAddr, "SOCKET_REUSEADDR", 0);
+RCCL_PARAM(SocketLinger, "SOCKET_LINGER", -1);
+
 static ncclResult_t socketProgressOpt(int op, struct ncclSocket* sock, void* ptr, int size, int* offset, int block, int* closed) {
   int bytes = 0;
   *closed = 0;
@@ -727,6 +730,17 @@ ncclResult_t ncclSocketInit(struct ncclSocket* sock, union ncclSocketAddress* ad
       ret = ncclSystemError;
       goto fail;
     }
+
+    // [RCCL] Runtime socket options
+    if (rcclParamSocketReuseAddr()) {
+      int opt = 1;
+      SYSCHECKGOTO(setsockopt(sock->fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt)), ret, fail);
+    }
+    int lingerParam = (int)rcclParamSocketLinger();
+    if (lingerParam > -1) {
+      linger linger_opt = { 1, lingerParam };
+      SYSCHECKGOTO(setsockopt(sock->fd, SOL_SOCKET, SO_LINGER, &linger_opt, sizeof(linger_opt)), ret, fail);
+    }
   } else {
     memset(&sock->addr, 0, sizeof(union ncclSocketAddress));
   }