Address an inconsistency: the mount.nfs command uses the glibc routines

Address an inconsistency:  the mount.nfs command uses the glibc routines
to manipulate /etc/mtab (setmntent) but, everything else in nfs-utils
uses a local private version (nfs_setmntent).  The local version does
some extra mangling of the mtab entries.

We should check what util-linux does these days to be sure, but for now,
let's make the mount.nfs command use the nfs_ variants of setmntent().

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>