ACL/SCO packet type and length validation only compiled under #ifdef DIAGNOSTIC

Summary

hci_acl_recv(:431-444) + hci_sco_recv(:841-854): checks that HCI packet type byte correct and m_pkthdr.len==hdr.length wrapped in #ifdef DIAGNOSTIC — absent in production/release kernels. Validated fields not re-read downstream so no direct OOB but silently accepting structurally malformed controller packets violates defense-in-depth masks mis-fragmentation fueling DF-0566/0567. Fix: make checks unconditional goto bad on mismatch.