You can switch partitions using this -
nvram set bootpartition=0 && nvram set partialboots=0 && nvram commit
bootpartition can be 0 or 1
You can see the partitions on LEDE for yourself - firmware is the first partition while failsafe is the second.
root@OpenWrt:/# cat /proc/mtd
dev: size erasesize name
mtd0: 00080000 00020000 "boot"
mtd1: 00100000 00020000 "nvram"
mtd2: 00080000 00020000 "nvram"
mtd3: 01d00000 00020000 "firmware"
mtd4: 003fffe4 00020000 "linux"
mtd5: 01900000 00020000 "ubi"
mtd6: 06100000 00020000 "failsafe"
Also, make sure to edit /etc/rc.local file where I force the bootpartition to 0