cfg80211: further limit wiphy names to 64 bytes

wiphy names were recently limited to 128 bytes by commit a7cfebcb
("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: a7cfebcb ("cfg80211: limit wiphy names to 128 bytes")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>