This is an evdev ioctl used to query a touchpad's multitouch state. On Linux it's marked as "read", but it passes the code of the attribute to get: on FreeBSD this requires the ioctl to be "read+write" otherwise the userland data does't make it to the kernel driver.
Without this, the evdev kernel driver returns EINVAL because it doesn't recognized the ioctl.
Bugzilla PR: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=225343