fabric: Remove mask fields from attribute structures

The mask field is intended to support forward and backward compatibility
changes.  Since libfabric is new, we will define more efficient
mechanisms for dealing with compatibility, such as using a simple
versioning scheme.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
fabric/man: Update man pages to remove attr mask

Update man pages to reflect mask fields being removed from
attributes.

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