loader: update symlink support in zfs reader

[tsoome]

Summary

As the current zfs file system is providing symlink via system attributes, need to update the code accordingly.

Test Plan

Tested by browsing and reading different symlinks and by using names like /usr/bin/../lib, bin/.., etc/., etc/./inet, ./bin

[avg]

LGTM

[smh]

sys/boot/zfs/zfsimpl.c

2273

All of the above are only used in == DMU_OT_SA case so could be moved into that block with char *p;

2294

Does the boot code make use of SET_ERROR, I'm guessing not?

2382

Missing space

[tsoome]

sys/boot/zfs/zfsimpl.c

2294

no, it does not.

[tsoome]

Fixes suggested by smh.

[smh]

sys/boot/zfs/zfsimpl.c

2282

Just spotted that if you invert the condition you get an arguably cleaner flow e.g.

 else {
    if ((dn->dn_flags & DNODE_FLAG_SPILL_BLKPTR) == 0)
        return (EIO);

    blkptr_t *bp = &dn->dn_spill;

    size = BP_GET_LSIZE(bp);
    ...
}

[tsoome]

svn update; and clean up the inverted if statement.

[smh]

LGTM

[allanjude]

Approved By: allanjude