socket2 0.4.1 does not compile on Haiku with feature `all`

[link2xt]

The problem is that since merging of #251 on this line KEEPALIVE_TIME is not defined on Haiku and OpenBSD:

socket2/src/sys/unix.rs

Line 871 in 877a789

getsockopt::<c_int>(fd, IPPROTO_TCP, KEEPALIVE_TIME)