rtlwifi: properly apply filter flags

commit 0baa0fd7
("rtlwifi: Convert core routines for addition of rtl8192se and
rtl8192de") removed setting HW_VAR_RCR, HW_VAR_MGT_FILTER and
HW_VAR_CTRL_FILTER. The last two are probably done because some hardware
does not support them. The first is probably a mistake. This patch adds
the missing set_hw_reg call.

For PCI support, rx_conf is not touched directly. Instead, get_hw_reg is
used to abstract between receive_config (for PCI) and rx_conf (for USB).

This was tested on a 10ec:8176 Realtek RTL8188CE (according to the
label on the mini-PCIe card). Before this patch, `iw wlan0 set monitor
otherbss` did not capture frames from other BSS's. After this patch, it
does print packets.

Tested-by: Peter Wu <lekensteyn@gmail.com>
Signed-off-by: Peter Wu <lekensteyn@gmail.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>