Save peer CSRK after ltk generation

Security level at stack side is determined after the LTK generation,
saving peer csrk info prior to this would result in saving security level as ZERO for peer CSRK info in to config file.
This can cause clearing the MITM_AUTH flag when CSRK info is loaded in the next BT session as security level is saved as ZERO for CSRK. Saving the peer CSRK after ltk generation would help in saving the right security level

Test: mmm packages/modules/Bluetooth
Test: Tested with Android wear where socket connections were failing due to no MITM_AUTH after bt reset.
Flag: com.android.bluetooth.flags.save_peer_csrk_after_ltk_gen
Bug: 362322766
Bug: 365567905

Change-Id: I7b9061db13cdcdbe3535c913dfd29f5a30449803