Maximum Bit Rate (MBR) Rule doesn't applicable for Non-GBR bearers it is only for Guaranteed Bit Rates.
For Non-GBR there are two different called bit rates available.
These are UE-AMBR (aggregate max bit rate) monitored by eNB, and APN-AMBR take care by P-GW the APN-AMBR parameter is provided by the PCRF (can be predefined in the PCEF too).
Note: that APN-AMBR is enforced by PCEF (PGW) for both Upstream and Downstream traffic for a particular APN. The first includes all the UE's non-GBR bearers and the second includes all the non-GBR bearers for a particular APN - e.g. IMS
