staging: rtl8723bs: replace deeply nested if-else with switch-case

staging: rtl8723bs: replace deeply nested if-else with switch-case

The main logic of the validate_recv_mgnt_frame() function is deeply
nested due to multiple if-else statements and additional block scope.
Fix this by replacing identical if-else with switch-case statements,
which will improve code readability and correct checkpatch.pl warnings
about line lengths.

Signed-off-by: Nikolay Kulikov <nikolayof23@gmail.com>
Link: https://patch.msgid.link/20260323150650.7168-2-nikolayof23@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>