Values in `ioctl` are given through a pointer, but ioctl's FIONBIO
implementation was interpreting this pointer as an integer directly.
This meant that programs using `ioctl` to set a file descriptor in
blocking mode met with incorrect behavior: they passed a non-null
pointer pointing to a value of 0, but the kernel interpreted the pointer
as a non-zero integer, thus making the file non-blocking.
This commit fixes this behavior by reading the value from the userspace
pointer and using that to set the non-blocking flag on the file
descriptor.
This bug was found while trying to run the openssl tool on serenity,
which used `ioctl` to ensure newly-created sockets are in blocking mode.
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