wifi: rtw89: use separated function to set RX filter

wifi: rtw89: use separated function to set RX filter

Normally use rtw89_write32_mask() with a consecutive bit mask, but mask of
RX filter B_AX_RX_FLTR_CFG_MASK is bits 31-22 and 15-0, which excludes bits
of B_AX_RX_MPDU_MAX_LEN_MASK (bits 21-16).

Though the original logic is well to set RX filter, change it to a separate
function to avoid the tricky design.

Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/20251113053459.34995-1-pkshih@realtek.com