nl80211: Increase maximum NL80211_ATTR_KEY_SEQ length to 16

WPI-SMS4 uses 16-octet PN field, so we need to allow longer key
sequence values to be configured.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>