wireshark: Fix int type of some virNetMessageHeader members

wireshark: Fix int type of some virNetMessageHeader members

Our virNetMessageHeader is a struct that's declared as follows:

  struct virNetMessageHeader {
      unsigned prog;
      unsigned vers;
      int proc;
      virNetMessageType type;
      unsigned serial;
      virNetMessageStatus status;
  };

Now, per RFC 4506 enums are also encoded as signed integers. This
means, that only 'prog', 'vers' and 'serial' are really unsigned
integers. The others ('proc', 'type' and 'status') are encoded as
signed integers. Fix their type when dissecting.

While at it, also follow latest trend in wireshark and switch
from guint32 to uint32_t.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>