Align radiotap structures in ral(4)

Currently all radiotap structures in ral(4) are packed, but are not
aligned, which causes ral based devices to crash when one does
'ifconfig wlan0 up' for a wlan interface with a ral wlandev on arches
that care about structure alignment (e.g., MIPS).

Adding an aligned attribute helps fix this problem and ral devices
can be properly brought up.

Reviewed by: adrian
Sponsored by: Smartcom - Bulgaria AD