dpdk: fix udp-encap for esp in transport mode

Now UDP encapsulation doesn't work in transport mode because:
 - the encrypt node misses filling of UDP header and it gets sent with
   all zeros;
 - the decrypt node misses filling of new IP header and it contains
   garbage data.

With this commit, fill UDP header during encryption and fill IP header
during decryption.

Change-Id: I87a7bd594f0e312b16d3e5eb19e568b4e3164d36
Type: fix
Signed-off-by: Alexander Chernavin <achernavin@netgate.com>