Revision 1.173 broke updating a mount from ro to rw.  Fix that by clearing the MNT_RDONLY flag if MNT_UPDATE is set and "ro" was not specified.
Revision 1.173 broke updating a mount from ro to rw.  Fix that by clearing
the MNT_RDONLY flag if MNT_UPDATE is set and "ro" was not specified.

Suggested by:	cognet

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase