rt2x00: Fix IEEE80211_TX_CTL_MORE_FRAMES handling

IEEE80211_TX_CTL_MORE_FRAMES indicates that more frames are queued for tx
but has nothing to do with fragmentation. Hence, don't set ENTRY_TXD_MORE_FRAG
but only ENTRY_TXD_BURST to not kick the tx queues immediately.

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>