sys/vfs/hammer: Don't let ioctl(HAMMERIOC_SET_PSEUDOFS) create PFS in PFS
hammer pfs-master|slave have been preventing users from creating
a PFS in non-root PFS, but since kernel HAMMER code also assumes
the parent inode of (non-root)PFS root inode has 0 for ip localization,
ioctl(HAMMERIOC_SET_PSEUDOFS) itself should avoid that too.
This commit doesn't affect HAMMER userspace commands because
hammer pfs-master|slave prevent creating a PFS in PFS prior to
calling ioctl(HAMMERIOC_SET_PSEUDOFS). It just makes better sense
to have this check in kernel space as well since one could write
its own userspace program that directly calls ioctl without using
hammer userspace code.
Also see
5b4785a6.