INT 21 - Phar Lap 386/DOS-Extender - SET REAL-MODE INTERRUPT VECTOR
AX = 2505h
CL = interrupt number
EBX = CS:IP of real-mode interrupt handler
Return: CF clear
Note:   this function is also supported by FlashTek X-32VM
SeeAlso: AX=2504h,INT 31/AX=0201h

See also: 212503

212505 - Phar Lap 386/DOS-Extender - SET REAL-MODE INTERRUPT VECTOR