After searching fer some answers / directions, I found out that OpenBSD Man Page is one of the place to go. After reading boot_config part of the man page, I go on and boot to 4.3 again. On the boot prompt I go and type "/bsd -c" to boot to User Kernel Config (UKC). It's something like this:
boot> /bsd -c
Then I disabled the ehci by typing:
UKC> disable ehci
After that 4.3 booted the kernel with ehci disabled. But then the booting problem got worst. My lcd went standby (the LED turned orange) and the HDD LED blinks rapidly. Hard reset AND hard boot didn't work. I had to turn the power off right from the power socket. So the culprit is not ehci (or maybe not JUST ehci?, I'm not sure right now.).
Take note that this UKC will retain the setting you changed per reboot. Means that when you rebooted, you need to change the UKC setting again or else it'll boot the default.