Relock Real Mode Region

Relocks a memory region that was previously declared as
pageable with the Mark Real Mode Region as Pageable function
(Int 31H Fn 0602H).

Call With:

   AX     = 0603H
   BX:CX  = starting linear address of memory to relock
   SI:DI  = size of region to relock (bytes)

Returns:

   if function successful
   Carry flag= clear

   if function unsuccessful
   Carry flag= set
   AX     = error code
           8002H   invalid state (region not marked as
                   pageable)
           8013H   physical memory unavailable
           8025H   invalid linear address (region is above 1
                   MB boundary)

Notes:

o  If the function returns an error, none of the memory has
   been relocked.
o  If the specified region overlaps part of a page at the
   beginning or end of the region, the page(s) will not be
   relocked.
o  This function is ignored by DPMI implementations that do
   not support virtual memory; the function will return the
   Carry flag clear to indicate success, but has no other
   effect.  DPMI hosts which support virtual memory may also
   choose to ignore this function, but such hosts must be
   able to handle page faults transparently at arbitrary
   points during a client's execution, including within
   interrupt and exception handlers.
o  If Function 0602H is implemented as a "no-operation" on a
   particular DPMI host, this function will likewise do
   nothing.  In other words, this function should not be
   used to lock memory, but only to restore the default
   state of the host's conventional memory locking.