mac802154: declare reduced mlme operations

According IEEE 802.15.4 standard each node can be either full functionality
device (FFD) or reduce functionality device (RFD). So 2 sets of operations
are needed. This patch declare RFD operations structure.

Signed-off-by: Alexander Smirnov <alex.bluesman.smirnov@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>