mount structure prefixes go from m_ to mnt_ and M_ to MNT_

mount structure prefixes go from m_ to mnt_ and M_ to MNT_

SCCS-vsn: sys/nfs/nfs_vnops.c 7.37
SCCS-vsn: sys/nfs/nfs_node.c 7.25
SCCS-vsn: sys/nfs/nfs_serv.c 7.18
SCCS-vsn: sys/nfs/nfs_socket.c 7.11
SCCS-vsn: sys/nfs/nfs_subs.c 7.22
SCCS-vsn: sys/nfs/nfs_vfsops.c 7.20
SCCS-vsn: sys/nfs/nfs_syscalls.c 7.13
SCCS-vsn: sys/nfs/nfsmount.h 7.4
SCCS-vsn: sys/sys/mount.h 7.13
SCCS-vsn: sys/kern/kern_acct.c 7.9
SCCS-vsn: sys/kern/kern_exec.c 7.22
SCCS-vsn: sys/miscfs/specfs/spec_vnops.c 7.26
SCCS-vsn: sys/kern/vfs_bio.c 7.27
SCCS-vsn: sys/kern/vfs_cluster.c 7.27
SCCS-vsn: sys/kern/vfs_lookup.c 7.21
SCCS-vsn: sys/kern/vfs_subr.c 7.42
SCCS-vsn: sys/kern/vfs_syscalls.c 7.46
SCCS-vsn: sys/kern/vfs_vnops.c 7.20
SCCS-vsn: sys/deprecated/kdb/kdb_print.c 7.18