api: fix vl_api_clnt_node process stack overflow

Type: fix

Some simple settings(e.g. bringing up an i40e/ice interface) through
vnat consume more than the currently available stack space.

This root cause of this issue is same with commit
b2dbb36fc265b8996fc7fa310dda447d5b0479cb "vlib: fix startup-config \
-process stack overflow" and commit 2fd44a00aa26188ca75f0accd734f2 \
1758c199bf "vlib: fix cli process stack overflow"

Signed-off-by: Chenmin Sun <chenmin.sun@intel.com>
Change-Id: I312e4fed96a679aa68b859e28a90a2a4b6eb0c6e
(cherry picked from commit a488f37559493657b59181c1212e57b3b9cc3689)

src/vlibmemory/vlib_api.c

@@ -418,6 +418,7 @@ VLIB_REGISTER_NODE (vl_api_clnt_node) =
   .type = VLIB_NODE_TYPE_PROCESS,
   .name = "api-rx-from-ring",
   .state = VLIB_NODE_STATE_DISABLED,
+  .process_log2_n_stack_bytes = 18,
 };
 /* *INDENT-ON* */