stream sni: fixed segfault that addr_conf->default_server is NULL

[chobits]

If INET6 is enabled, ngx_stream_add_addrs6 is runned instead of ngx_stream_add_addrs. The stream sni logic forgot to initialize addr_conf->default_server in ngx_stream_add_addrs6().

[chobits]

cc @mrpre

segfault found by tests/nginx-tests/nginx-tests/stream_variables.t

Program received signal SIGSEGV, Segmentation fault.                [9/1955]ngx_stream_init_connection (c=0x558215485e58)
    at src/stream/ngx_stream_handler.c:130
130         s->main_conf = ((ngx_stream_core_srv_conf_t*)addr_conf->default_server)->ctx->main_conf;                                                    (gdb) p addr_conf->default_server
$1 = (void *) 0x0                                                          
 (gdb) bt                                                                    #0  ngx_stream_init_connection (c=0x558215485e58)
    at src/stream/ngx_stream_handler.c:130
#1  0x0000558213cc8a08 in ngx_event_accept (ev=0x5582154a4290)
    at src/event/ngx_event_accept.c:329
#2  0x0000558213cdc696 in ngx_epoll_process_events (cycle=0x55821546b6e0,
    timer=60000, flags=1) at src/event/modules/ngx_epoll_module.c:972
#3  0x0000558213cc4e20 in ngx_process_events_and_timers (
    cycle=0x55821546b6e0) at src/event/ngx_event.c:260
#4  0x0000558213cd99b2 in ngx_worker_process_cycle (cycle=0x55821546b6e0,
    data=0x0) at src/os/unix/ngx_process_cycle.c:811

[chobits]

After this commit, case passed.

$ sh runtest.sh tests/nginx-tests/nginx-tests/stream_variables.t
tests/nginx-tests/nginx-tests/stream_variables.t
tests/nginx-tests/nginx-tests/stream_variables.t .. ok
All tests successful.
Files=1, Tests=10,  0 wallclock secs ( 0.01 usr  0.00 sys +  0.06 cusr  0.05 csys =  0.12 CPU)
Result: PASS

[chobits]

approved by @mrpre

[harry-xm]

@chobits Would you mind renaming NGX_STREAM_SNI to T_NGX_STREAM_SNI? This seems to be a Tengine-specific flag.

[chobits]

@harry-xm thats ok to change it to T_XXX