mac80211: allow drivers to set max MTU

Make it possibly for drivers to adjust the default max_mtu
by storing it in the hardware struct and using that value
for all interfaces.

Signed-off-by: Wen Gong <wgong@codeaurora.org>
Link: https://lore.kernel.org/r/1567738137-31748-1-git-send-email-wgong@codeaurora.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/mac80211.h

@@ -2463,6 +2463,8 @@ enum ieee80211_hw_flags {
  *
  * @weight_multiplier: Driver specific airtime weight multiplier used while
  *	refilling deficit of each TXQ.
+ *
+ * @max_mtu: the max mtu could be set.
  */
 struct ieee80211_hw {
 	struct ieee80211_conf conf;
@@ -2500,6 +2502,7 @@ struct ieee80211_hw {
 	u8 max_nan_de_entries;
 	u8 tx_sk_pacing_shift;
 	u8 weight_multiplier;
+	u32 max_mtu;
 };
 
 static inline bool _ieee80211_hw_check(struct ieee80211_hw *hw,

net/mac80211/iface.c

@@ -1876,7 +1876,7 @@ int ieee80211_if_add(struct ieee80211_local *local, const char *name,
 
 		/* MTU range: 256 - 2304 */
 		ndev->min_mtu = 256;
-		ndev->max_mtu = IEEE80211_MAX_DATA_LEN;
+		ndev->max_mtu = local->hw.max_mtu;
 
 		ret = register_netdevice(ndev);
 		if (ret) {

net/mac80211/main.c

@@ -639,6 +639,7 @@ struct ieee80211_hw *ieee80211_alloc_hw_nm(size_t priv_data_len,
 					 IEEE80211_RADIOTAP_VHT_KNOWN_BANDWIDTH;
 	local->hw.uapsd_queues = IEEE80211_DEFAULT_UAPSD_QUEUES;
 	local->hw.uapsd_max_sp_len = IEEE80211_DEFAULT_MAX_SP_LEN;
+	local->hw.max_mtu = IEEE80211_MAX_DATA_LEN;
 	local->user_power_level = IEEE80211_UNSET_POWER_LEVEL;
 	wiphy->ht_capa_mod_mask = &mac80211_ht_capa_mod_mask;
 	wiphy->vht_capa_mod_mask = &mac80211_vht_capa_mod_mask;