cfg80211: further limit wiphy names to 64 bytes

wiphy names were recently limited to 128 bytes by commit a7cfebcb7594
("cfg80211: limit wiphy names to 128 bytes").  As it turns out though,
this isn't sufficient because dev_vprintk_emit() needs the syslog header
string "SUBSYSTEM=ieee80211\0DEVICE=+ieee80211:$devname" to fit into 128
bytes.  This triggered the "device/subsystem name too long" WARN when
the device name was >= 90 bytes.  As before, this was reproduced by
syzbot by sending an HWSIM_CMD_NEW_RADIO command to the MAC80211_HWSIM
generic netlink family.

Fix it by further limiting wiphy names to 64 bytes.

Reported-by: syzbot+e64565577af34b3768dc@syzkaller.appspotmail.com
Fixes: a7cfebcb7594 ("cfg80211: limit wiphy names to 128 bytes")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/uapi/linux/nl80211.h

@@ -2698,7 +2698,7 @@ enum nl80211_attrs {
 #define NL80211_ATTR_KEYS NL80211_ATTR_KEYS
 #define NL80211_ATTR_FEATURE_FLAGS NL80211_ATTR_FEATURE_FLAGS
 
-#define NL80211_WIPHY_NAME_MAXLEN		128
+#define NL80211_WIPHY_NAME_MAXLEN		64
 
 #define NL80211_MAX_SUPP_RATES			32
 #define NL80211_MAX_SUPP_HT_RATES		77