vsock: add missing vsockmon header reserved field

vsock: add missing vsockmon header reserved field

The vsockmon packet header is defined in <linux/vsockmon.h> as follows:

struct af_vsockmon_hdr {
	__le64 src_cid;
	__le64 dst_cid;
	__le32 src_port;
	__le32 dst_port;
	__le16 op;			/* enum af_vsockmon_op */
	__le16 transport;		/* enum af_vsockmon_transport */
	__le16 len;			/* Transport header length */
	__u8 reserved[2];
};

The vsock dissector forgot to include the 2-byte reserved field.  This
caused the transport header and payload that follow the vsockmon header
to contain junk data.

Change-Id: I0e7e6f1d9ad96ab339bd070c1becf43bc7e6a6b1
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-on: https://code.wireshark.org/review/22612
Reviewed-by: Michael Mann <mmann78@netscape.net>
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>