cnat: Add sctp support

This patch adds SCTP support in the CNat translation primitives.
It also exposes a clib_crc32c_with_init function allowing to set
the init value to start the crc32 with instead of 0.

Type: feature

Change-Id: I86add4cfcac08f2a5a34d1e1841122fafd349fe7
Signed-off-by: Nathan Skrzypczak <nathan.skrzypczak@gmail.com>

src/plugins/cnat/cnat_types.h

@@ -55,6 +55,17 @@
 
 #define MIN_SRC_PORT ((u16) 0xC000)
 
+typedef struct
+{
+  /* Source and destination port. */
+  u16 src_port, dst_port;
+
+  /* Random value to distinguish connections. */
+  u32 verification_tag;
+
+  u32 checksum;
+} sctp_header_t;
+
 typedef enum cnat_trk_flag_t_
 {
   /* Endpoint is active (static or dhcp resolved) */