l2cap: Fix for L2CAP Credit Based Reconfigure Request with MPS

Stack should accept L2CAP Credid Based Reconfigure Reqest with smaller MPS
 than initiated MPS for one channel
Test : verified with L2CAP/ECFC/BI-07-C and L2CAP/ECFC/BV-25-C

Change-Id: I3dc3eff2ae3d58ec9144282b12e2b472211e01fa