Introducing the function that does the ATM cell alignment, and
modifying tc_calc_rtable() to use this based upon a linklayer
parameter.

Modified from original to use constants from atm.h and
fix all the usages of rtable in same patch.
Signed-off-by: Jesper Dangaard Brouer <hawk@comx.dk>
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>