tmf: Fix some critical and major Sonar warnings

tmf: Fix some critical and major Sonar warnings

Security - Array is stored directly
Naming - Suspicious constant field name
Performance - Should be a static inner class

Change-Id: Ifeed507f41dd40562a8863e2847bcd39e7c44c5c
Signed-off-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-on: https://git.eclipse.org/r/88797
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-by: Hudson CI