wimax: fix duplicate initializer warning

gcc -Wextra points out multiple fields that use the same index '1'
in the wimax_gnl_policy definition:

net/wimax/stack.c:393:29: warning: initialized field overwritten [-Woverride-init]
net/wimax/stack.c:397:28: warning: initialized field overwritten [-Woverride-init]
net/wimax/stack.c:398:26: warning: initialized field overwritten [-Woverride-init]

This seems to work since all four use the same NLA_U32 value, but it
still appears to be wrong. In addition, there is no intializer for
WIMAX_GNL_MSG_PIPE_NAME, which uses the same index '2' as
WIMAX_GNL_RFKILL_STATE.

Johannes already changed this twice to improve it, but I don't think
there is a good solution, so try to work around it by using a
numeric index and adding comments.

Fixes: 3b0f31f2 ("genetlink: make policy common to family")
Fixes: b61a5eea ("wimax: use genl_register_family_with_ops()")
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>