transportHandler: Separate some util functions to hpp

When I implemented the transport oem command as suggested
in [1], I found that transporthandler.cpp already implements
a lot of util functions that are useful for implementing
transporthandler_oem.cpp

So, there is this patch, which moves a lot of functions
already implemented in cpp to hpp, so that transporthandler_oem.cpp can use them.
I believe it will be useful for others to implement the transport oem commands as well.

[1] https://github.com/openbmc/phosphor-host-ipmid/blob/master/transporthandler.cpp#L1264

Signed-off-by: John Wang <wangzhiqiang.bj@bytedance.com>
Change-Id: I580f005df3622ea9340cd303040d98a5527de55e
2 files changed