Properly format NAME subsection of zfs/zpool subcommands

Use proper names (i.e. zfs-allow and zpool-add) in NAME subsections
of zfs/zpool subcommands instead of current "pretty-printed" ones as
makewhatis utilities (or some implementations of it, namely the one
from mandoc suite used in FreeBSD) look not only at the document title
but also in NAME subsection, adding zfs(8)/zpool(8) to search results
which is not correct. (Common sense and other utilities splitting
subcommands in multiple man pages, e.g. git, do the same.)

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: xtouqh <xtouqh@hotmail.com>
Closes #11086

man/man8/zpool-export.8

@@ -31,10 +31,10 @@
 .Dt ZPOOL-EXPORT 8
 .Os
 .Sh NAME
-.Nm zpool Ns Pf - Cm export
+.Nm zpool-export
 .Nd Exports the given ZFS storage pools from the system
 .Sh SYNOPSIS
-.Nm
+.Nm zpool
 .Cm export
 .Op Fl a
 .Op Fl f
@@ -42,7 +42,7 @@
 .Sh DESCRIPTION
 .Bl -tag -width Ds
 .It Xo
-.Nm
+.Nm zpool
 .Cm export
 .Op Fl a
 .Op Fl f
@@ -60,7 +60,7 @@ A pool can not be exported if it has a shared spare that is currently being
 used.
 .Pp
 For pools to be portable, you must give the
-.Nm
+.Nm zpool
 command whole disks, not just partitions, so that ZFS can label the disks with
 portable EFI labels.
 Otherwise, disk drivers on platforms of different endianness will not recognize