New code from lwip project

lwip repo:
8216303 revert accidentally committed test code
6c7357b DNS: minor coding style fix: pEntry -> entry
13add69 Merge branch 'master' of git.sv.gnu.org:/srv/git/lwip
a491aa0 DNS: split request callback information from actual DNS table to be able to optimize memory usage for multiple parallel requests (and clean up the code a bit)