This patch fixes the "rm_audit_sync_block: sync block corruption" panic due to
not checking loopback early in boot. We spin through the write_sync loop before
the data is written and panic in the audit code. Then, the data subsequently 
gets written before the dump is written. In the case of VHUB set up, only part
of the data is written. Thus, the write_sync loop's condition was modify to
accomodiate this.

Panic String:
   rm_audit_sync_block: sync block corruption

   Stack trace:

       0 boot                 src/kernel/arch/alpha/machdep.c : 2964
       1 panic                src/kernel/bsd/subr_prf.c : 1432
       2 rm_crash_nodes       src/kernel/rm/rm_error.c : 2467
       3 rm_panic             src/kernel/rm/rm_error.c : 1915
       4 rm_audit_sync_block  src/kernel/rm/rm_error.c : 1457
       5 rm_write_sync        src/kernel/rm/rm_error.c : 1820
       6 rm_push_shared_data  src/kernel/rm/rm_error.c : 862
       7 rm_eh_init_shared_data_req  src/kernel/rm/rm_prail.c : 928
       8 rm_prail_int         src/kernel/rm/rm_prail.c : 1152
       9 rm_int               src/kernel/rm/rm_prail.c : 1117
      10 Mchan_isr            src/kernel/io/dec/pci/mchan.c : 8077
      11 _XentInt             src/kernel/arch/alpha/locore.s : 1654
      12 idle_thread          src/kernel/kern/sched_prim.c : 4535
