dynamic settings may fail when slice involving

[RocFang]

Hello! @spacewander

Since https://hg.nginx.org/nginx/rev/d16ba0ea3434 ，
Subrequests of slice module will bypass phases which come before content handler, and may trigger some confusing behaviors for some dynamic settiings, especialy proxy settings. For example #35 .

The safe way maybe set the according attributes of ngx_http_apisix_ctx_t again to ctx->sr right after ngx_http_subrequest in ngx_http_slice_filter_module.c .

It's not a bug report, just a mention.

[spacewander]

Thanks for your suggestion!

[membphis]

many thx for your nice mention @RocFang

[RocFang]

@membphis It's a pleasure. :)