vfs_export: Simplify vfs_export_lookup

[manu]

Summary

If the filesystem is not exported directly return NULL.
If no address is given and filesystem is exported using some default one
return it directly, if it doesn't have a default one directly return NULL.

MFC After: 1 week
Sponsored-By: Gandi.net

[kib]

sys/kern/vfs_export.c

465

if ((mp->mnt_flag & MNT_DEFEXPORTED) != 0)

467

You do not need else

473

Use 4-spaces indent for continuation.

474

if (np != NULL && (np->...->rn_flags & RNF_ROOT) != 0)

475

You might return (NULL) there directly as well.

[manu]

Address kib's comments.

[kib]

sys/kern/vfs_export.c

487

if (np != NULL && ..