wifi: (fixes #929) Fix error with compilers clang-6, clang-10 and gcc-8
Fix errors in the Wi-Fi module reported in the weekly pipelines.
../src/wifi/test/wifi-emlsr-test.cc:1493:18: error: no member named 'for_each_n' in namespace 'std'
std::for_each_n(m_staMacs.cbegin(), m_nEmlsrStations, [&](auto&& staMac) {
~~~~~^
Fix #929 (closed)