staging: rtl8192e: Use standard function in softmac_mgmt_xmit()

Use standard function ieee80211_is_beacon() to avoid proprietary code to
identify beacon and to increase readability in softmac_mgmt_xmit() and
_rtl92e_translate_rx_signal_stats()

Signed-off-by: Philipp Hortmann <philipp.g.hortmann@gmail.com>
Link: https://lore.kernel.org/r/bd648e8e3c9c93c7944b72778ef7288973d8386e.1694546300.git.philipp.g.hortmann@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>