The test in configure checks for struct mmsghdr in sys/socket.h, but actual source (net/l2tpv3.c) includes a linux-specific header, linux/ip.h. This fails on at least kFreeBSD (Debian with FreeBSD header and glibc), because glibc declares mmsghdr but does not provide linux/ip.h.
Probably the configure test should also include this linux-specific header. At least this is what I plan to do to fix the build failure with 2.1. Thanks, /mjt
