Mark functions as static

Mark functions used only in the same translation unit as static. This
only includes functions that do not have a prototype in a header file
either.

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Closes #10470

lib/libzfs/libzfs_mount.c

@@ -822,7 +822,7 @@ zfs_unshare_smb(zfs_handle_t *zhp, const char *mountpoint)
 /*
  * Same as zfs_unmountall(), but for NFS and SMB unshares.
  */
-int
+static int
 zfs_unshareall_proto(zfs_handle_t *zhp, zfs_share_proto_t *proto)
 {
 	prop_changelist_t *clp;