staging: rtl8192e: Use standard function in rtllib_rx_check_duplicate()

Use standard function ieee80211_is_beacon() to avoid proprietary code and
to increase readability.

Signed-off-by: Philipp Hortmann <philipp.g.hortmann@gmail.com>
Link: https://lore.kernel.org/r/b74b6ef5e266504b9e3d84495bcd8fe4978b4ded.1694546300.git.philipp.g.hortmann@gmail.com


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