Kernel: Remove SmapDisabler in sys$ioctl()

Use copy_{to,from}_user() in the various File::ioctl() implementations
instead of disabling SMAP wholesale in sys$ioctl().

This patch does not port IPv4Socket::ioctl() to those API's since that
will be more involved. That function now creates a local SmapDisabler.

Kernel/Syscalls/ioctl.cpp

@@ -34,7 +34,6 @@ int Process::sys$ioctl(int fd, unsigned request, FlatPtr arg)
     auto description = file_description(fd);
     if (!description)
         return -EBADF;
-    SmapDisabler disabler;
     return description->file().ioctl(*description, request, arg);
 }