Workaround clang++ concepts crash

Instead of capturing everything by reference implicitly, capture just
the necessary variables. This avoids a clang++ crash in its code for
handling C++20 concepts.

Bug: 335969721
Test: m bluetooth_packetgen
Flag: EXEMPT, refactoring
Change-Id: Id94310cd5b02d38a866be7af5a37789dbc094d9f