bbf: Made dscp2pbit vendor extension configurable through tr-181
set/get function to set and get dscp to p-bit mapping in the uci file (Support to set mapping of dscp value 0 to 63).
The set function takes p-bit values in comma separated form and the position of the p-bit value denotes its mapping to DSCP value.
example: "2,3,4,0,0,1,5" uci list: list dscp2pbit '0:2' list dscp2pbit '1:3' list dscp2pbit '2:4' list dscp2pbit '3:0' list dscp2pbit '4:0' list dscp2pbit '5:1' list dscp2pbit '6:5'
format 'x:y' x=DSCP y=p-bit