Merge branch 'ew/daemon-socket-keepalive' into maint

Recent update to "git daemon" tries to enable the socket-level KEEPALIVE, but when it is spawned via inetd, the standard input file descriptor may not necessarily be connected to a socket. Suppress an ENOTSOCK error from setsockopt(). * ew/daemon-socket-keepalive: Windows: add missing definition of ENOTSOCK daemon: ignore ENOTSOCK from setsockopt