mds/limits.h: add some limits
mds/limits.h: add some limits

Add RF_INVAL_MID, RF_INVAL_FSID, RF_MAX_MDS

Signed-off-by: Colin McCabe <3142ce8a0bdba4a38073365893e6b74f72d9c512@alumni.cmu.edu>

cmccabe/redfish,cmccabe/redfish,cmccabe/redfish,cmccabe/redfish,cmccabe/redfish