packets: Un-inline functions needed by DDlog.

packets: Un-inline functions needed by DDlog.

DDlog uses these functions from Rust, but Rust can't use inline
functions (since it doesn't compile C headers but only links
against a C-compatible ABI).  Thus, move the implementations
of these functions to a .c file.

I don't think any of these functions is likely to be an
important part of a "fast path" in OVS, but if that's wrong,
then we could take another approach.

Signed-off-by: Leonid Ryzhyk <lryzhyk@vmware.com>
Co-authored-by: Ben Pfaff <blp@ovn.org>
Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Numan Siddique <numans@ovn.org>