I, like many of the other replies, am not fully understanding what you are trying to do here. This data is available via existing tools.
But... if you are interested in rolling your own* you can write against the PerfStat API. Virtually all the performance stats on AIX come from this source. It is really easy to write against and the documentation on InfoCenter should be sufficient for anyone who can read/write C.
[* Insert disclaimer here: "Those who do not know of a Unix utility are destined to re-write it, badly."]
There is some sample source for the (netinterface portion of) LibPerfStat API here:
ifstat
(See a link to the source at the very bottom of the page)
The page also includes some commentary on syntax problems in the AIX supplied header files for LibPerfStat as encountered with GCC.