io_uring/cmd_net: split ioctl code out of io_uring_cmd_sock()

io_uring/cmd_net: split ioctl code out of io_uring_cmd_sock()

io_uring_cmd_sock() originally supported two ioctl-based cmd_op
operations. Over time, additional operations were added with tail calls
to their helpers.

This approach resulted in the new operations sharing an ioctl check
with the original operations.

io_uring_cmd_sock() now supports 6 operations, so let's move the
implementation of the original two into their own helper, reducing
io_uring_cmd_sock() to a simple dispatcher.

Signed-off-by: Asbjørn Sloth Tønnesen <ast@fiberby.net>
Signed-off-by: Jens Axboe <axboe@kernel.dk>