Fixes for iOS

[jpstotz]

Thanks for the script, it was very helpful, but I ran into some small problems, that are fixed by this PR:

On iOS 16 I had the problem that the transmitted data was not properly printed, as data.toString() does truncate the data if it is longer than about 20 bytes. Fixed by using the custom JS buf2hex function.

I also had the problem that received notifications were shown twice, therefore I changed the code to use the value property setter instead of getter.