Implement a simple block device on-top of LNet.

This is implemented as two drivers: lnet_host.ko (client) and lnet_target.ko (server). The target allocates an array of pages and registers them as passive RDMAs. The host registers a block device and devices block requests to the target as LNetGet() and LNetPut(). There is a one-to-one mapping between O_DIRECT block IOs and LNet network requests.

The LNet block driver aims to implement the simplest LNet service possible. With some additional optimization, this could serve as an alternative to LNet selftest.