pfkeyv2 : proto feild in address extension

hi
while trying to add protocol entry into the sadb from used space i saw in
the pfkeyv2 code that the proto element within the address extension has
not been used.The pf key v2  RFC also gives it  as a MUST condition, that
the transport layer protocol should be given within the proto feild of the
address extension.

i wanted to know why proto field within the address extension has not been
used by freeswan to implement protocol level granularity, i havent tried
doing this myself yet, so i wanted to enquire if there are some problems to
it.

thanks and regards.