[v1.8] Make TensorPipe work around bug in old versions of libibverbs (pytorch#52615)

The bug affects PyTorch users who meet two conditions:
- they have an old version of libibverbs installed (the userspace library), namely older than v25, which dates from Jul 29, 2019;
- but they do _not_ have an InfiniBand kernel module loaded.

In those cases they will experience a crash (uncaught exception) happening when initializing RPC, mentioning an "unknown error -38".

There is a workaround, which is for those users to activate a killswitch (which is private and undocumented) to disable the `ibv` backend of TensorPipe.

Author: lw