Update net_test.c
Update net_test.c

申请内存失败时，直接return，此前代码goto _exit进行rt_free空指针，会造成内存泄漏
nongxiaoming/rt-thread,RT-Thread/rt-thread,nongxiaoming/rt-thread,nongxiaoming/rt-thread,ArdaFu/rt-thread,nongxiaoming/rt-thread,RT-Thread/rt-thread,geniusgogo/rt-thread,ArdaFu/rt-thread,armink/rt-thread,armink/rt-thread,hezlog/rt-thread,hezlog/rt-thread,nongxiaoming/rt-thread,ArdaFu/rt-thread,geniusgogo/rt-thread,armink/rt-thread,ArdaFu/rt-thread,ArdaFu/rt-thread,hezlog/rt-thread,weety/rt-thread,hezlog/rt-thread,armink/rt-thread,armink/rt-thread,weety/rt-thread,geniusgogo/rt-thread,RT-Thread/rt-thread,weety/rt-thread,ArdaFu/rt-thread,weety/rt-thread,RT-Thread/rt-thread,hezlog/rt-thread,hezlog/rt-thread,geniusgogo/rt-thread,nongxiaoming/rt-thread,weety/rt-thread,RT-Thread/rt-thread,nongxiaoming/rt-thread,ArdaFu/rt-thread,armink/rt-thread,geniusgogo/rt-thread,weety/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread,weety/rt-thread,armink/rt-thread,geniusgogo/rt-thread,geniusgogo/rt-thread,hezlog/rt-thread