map gbp papi: match endianess of f64

map gbp papi: match endianess of f64

clib_net_to_host_f64, clib_host_to_net_f64 are now implemented as '=',
https://gerrit.fd.io/r/#/c/20406/  set papi to match.
- all f64 api references are now wrapped with
  clib_net_to_host_f64 or clib_host_to_net_f64.

IEEE f64 endianess is not defined.  If clib_net_to_host_f64 and
clib_host_to_net_f64 are later defined in VPP as big-endian, it is
a single character change in the papi vpp_serializer.

Note: This breaks the api in a manner that would not be detected by
the flag day initiative.  The scope is small.  This only impacts map.api,
which applied the u64 transformation, while the gbp api uses '='.

The implementation of "=" raises issues for the papi socket implementation
if used between systems of differing endianess.  See Vratko's comments.

- Added get_f64_endian_value() to api to allow client to verify endianess of f64's.

Type: fix
Depends-on: https://gerrit.fd.io/r/#/c/20484/

Change-Id: I00fc64a6557ba0190398df211aa0ea5c7eb101df
Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>