sr: fix prefix_len type parsing

prefix_len is parsed using '%u' format requiring an integer.

Type: fix

Change-Id: I9f31fa60e80d4f45fe456f3fd6c94f123cfc99ea
Signed-off-by: Benoît Ganne <bganne@cisco.com>
diff --git a/src/vnet/srv6/sr_localsid.c b/src/vnet/srv6/sr_localsid.c
index 67e8005..f632415 100644
--- a/src/vnet/srv6/sr_localsid.c
+++ b/src/vnet/srv6/sr_localsid.c
@@ -328,7 +328,7 @@
   vnet_main_t *vnm = vnet_get_main ();
   ip6_sr_main_t *sm = &sr_main;
   u32 sw_if_index = (u32) ~ 0, vlan_index = (u32) ~ 0, fib_index = 0;
-  u16 prefix_len = 0;
+  int prefix_len = 0;
   int is_del = 0;
   int end_psp = 0;
   ip6_address_t resulting_address;