Mozilla/5.0 (Windows NT 6.1; rv:38.0) Gecko/20100101 Thunderbird/38.7.2
You can have multiple connections with raw api. See httpd_raw example in
contrib tree (1.4.1) or httpd in apps (git head).
If you want to use lwIP in a multi-threaded environment, your best bet
is to use netconn or socket APIs (unless you restrict all calls within a
thread or implement a basic version of what netconn does yourself...)