New code from lwip project

lwip repo:
c065427 fixed bug #35928 BSD sockets functions must set errno for POSIX-compliance (patch by Mason)

lwip-contrib repo:
bc4a7f9 httpd: fix that http_write() returns 1 in "length" when not sending because of sndbuf/sndqueuelen
16167a2 Fixed bug #31948 httpd: Improving HTTP Server performance when SSI is enabled