odp-util: Fix alignment when scanning Geneve attributes.

odp-util: Fix alignment when scanning Geneve attributes.

Clang complains about the fact that we use a byte array to scan
Geneve attributes into since there are different alignment requirements:

lib/odp-util.c:2936:30: error: cast from 'uint8_t *' (aka 'unsigned char *') to

      'struct geneve_opt *' increases required alignment from 1 to 2

      [-Werror,-Wcast-align]

    struct geneve_opt *opt = (struct geneve_opt *)key->d;

                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~

We can instead treat this as an array of Geneve option headers to
ensure we get the right alignment and then there are no need for
casts.

Reported-by: Joe Stringer <joestringer@nicira.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>
Acked-by: Joe Stringer <joestringer@nicira.com>