Samsung Galaxy 7" (GT-P6210) USB debugging is not detecting in Linux?
When adb shows devices as ???????????? it's usually a permission problem and the usb device file. Your udev rules doesn't seem right. Make sure that you have udev configured to something like this:

SUBSYSTEM=="usb", SYSFS{idVendor}=="04e8", MODE="0666"


Where 04e8 is Samsung's USB Vendor ID.

Under Linux there is also an adb_usb.ini from the SDK where you have to add the vendor IDs:

~/.android/adb_usb.ini

# ANDROID 3RD PARTY USB VENDOR ID LIST -- DO NOT EDIT.
# USE 'android update adb' TO GENERATE.
# 1 USB VENDOR ID PER LINE.
0x17ef
0x1949