rsocket: Use configuration files to specify default settings

Give an administrator control over the default settings
used by rsockets.  Use files under rdma/rsocket as shown:

mem_default - default size of receive buffer
wmem_default - default size of send buffer
sqsize_default - default size of send queue
rqsize_default - default size of receive queue
inline_default - default size of inline data

If configuration files are not available, rsockets will continue to
use internal defaults.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>