staging: rtl8723bs: removed function prototypes and made statics in core/rtw_recv.c

staging: rtl8723bs: removed function prototypes and made statics in core/rtw_recv.c

fix the following checkpatch issue:

WARNING: externs should be avoided in .c files
1190: FILE: drivers/staging/rtl8723bs/core/rtw_recv.c:1190:
+signed int validate_recv_mgnt_frame(struct adapter *padapter, union recv_frame *precv_frame);

removed function prototypes and made statics

moved two static function definitions before their usage
to make code compile

Signed-off-by: Fabio Aiuto <fabioaiuto83@gmail.com>
Link: https://lore.kernel.org/r/e40951ad0d3ba103b1551e8f2e54c7bc45563346.1616503354.git.fabioaiuto83@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>