Fix multi-link llstat parsing in wifi legacy hal

Multi-link llstat parsing codes in wifi legacy hal, specifically
'copyLinkStat' and 'copyPeerInfo', pass the output container parameter
'std::vector<>' by value instead of by reference. The result is the
copied 'LinkStats' list and 'WifiPeerInfo' list are discarded when
'copyLinkStat' and 'copyPeerInfo' return. The empty links list are
passed to framework and fails validity check in Wi-Fi framework and
leads to system server crash.

Fix this issue by passing 'stats' and 'peers' by reference.

Bug: 269049672
Test: Manual Test with multi-link llstat implementation integrated
Change-Id: If8c366213af2ffcb9f7b3c904e1541ed0ac2fea4