mpls: fix default mpls lb hash config

In case of multiple path within tunnel, mpls lookup node
computes lb hash with mpls_compute_flow_hash config value 0,
so only mpls label and l4 ports gets accounted, not 5-tuple.
This leads to flow traffic polarization and disbalance over
mpls paths.

Use mpls hash config from lb instead, usually it'll be
MPLS_FLOw_HASH_DEFAULT with 5-tuple plus flowlabel.
As optimization, fix flow hash reuse from the previous lookup
node if present, like ip_lookup does. Previously mpls lookup
always calcs the hash.
Test lb distribution for both cases.

Also, use the same flow hash hex format in ip4/ip6 and mpls
traces for easier reading, most code changes is due fixstyle
formatting.

Type: fix
Signed-off-by: Vladislav Grishenko <themiron@yandex-team.ru>
Change-Id: Ib89e1ab3edec14269866fe825a3e887d6c817b7c
diff --git a/src/vnet/ip/ip6_forward.c b/src/vnet/ip/ip6_forward.c
index 06c473b..48fb633 100644
--- a/src/vnet/ip/ip6_forward.c
+++ b/src/vnet/ip/ip6_forward.c
@@ -948,8 +948,7 @@
   ip6_forward_next_trace_t *t = va_arg (*args, ip6_forward_next_trace_t *);
   u32 indent = format_get_indent (s);
 
-  s = format (s, "%Ufib:%d adj:%d flow:%d",
-	      format_white_space, indent,
+  s = format (s, "%Ufib:%d adj:%d flow:0x%08x", format_white_space, indent,
 	      t->fib_index, t->adj_index, t->flow_hash);
   s = format (s, "\n%U%U",
 	      format_white_space, indent,