brcmsmac: fix alignment constraints

sturct d11txh contains a ieee80211_rts structure, which is required to
have at least two byte alignment, and this conflicts with the __packed
attribute:

drivers/net/wireless/broadcom/brcm80211/brcmsmac/d11.h:786:1: warning: alignment 1 of 'struct d11txh' is less than 2 [-Wpacked-not-aligned]

Mark d11txh itself as having two-byte alignment to ensure the
inner structure is properly aligned.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210204162852.3219572-1-arnd@kernel.org

drivers/net/wireless/broadcom/brcm80211/brcmsmac/d11.h

@@ -783,7 +783,7 @@ struct d11txh {
 	u8 RTSPhyHeader[D11_PHY_HDR_LEN];	/* 0x2c - 0x2e */
 	struct ieee80211_rts rts_frame;	/* 0x2f - 0x36 */
 	u16 PAD;		/* 0x37 */
-} __packed;
+} __packed __aligned(2);
 
 #define	D11_TXH_LEN		112	/* bytes */