Use reserve for BQR data

Reserve enough space for the event and header to be reconstructed
and passed to the callbacks.  An extra byte is added for backward
compatibility until PDL is pushed farther up in the stack.

Bug: 322230000
Test: mma -j32
Flag: EXEMPT, no logical change
Change-Id: Ifa7caeaeaa558520301805fa5a6631567403c608