rsocket: Use configuration files to specify default settings

rsocket: Use configuration files to specify default settings

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

mem_default - default size of receive buffer
mem_max - max size of the receive buffer (restricts setsockopt)
wmem_default - default size of send buffer
wmem_max - max size of the send buffer (restricts setsockopt)
sqsize_default - default size of send queue
sqsize_max - max size of send queue (restricts setsockopt)
rqsize_default - default size of receive queue
rqsize_max - max size of receive queue (restricts setsockopt)
inline_default - default size of inline data
inline_max - max size of inline data (restricts setsockopt)

If configuration files are not available, rsockets will continue to
use internal defaults, with maximums limited by hardware.

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