vppapigen: add endian_string for f64

Type: fix

Change-Id: I35838baea21ead4a3f45d998ff225a513781d7ee
Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>
diff --git a/src/tools/vppapigen/vppapigen_c.py b/src/tools/vppapigen/vppapigen_c.py
index 93d14f3..19efc99 100644
--- a/src/tools/vppapigen/vppapigen_c.py
+++ b/src/tools/vppapigen/vppapigen_c.py
@@ -228,6 +228,7 @@
     'i16': 'clib_net_to_host_u16',
     'i32': 'clib_net_to_host_u32',
     'i64': 'clib_net_to_host_u64',
+    'f64': 'clib_net_to_host_u64',
 }