Remove assertion on output length for getsockopt.

POSIX allows `getsockopt` to set `*option_len` to a smaller value if
necessary. Windows will set `*option_len` to 1 for boolean options even
when the caller passes a `BOOL` (`int`) with `*option_len` as 4.

Author: chrisnc

library/std/src/sys_common/net.rs

@@ -87,7 +87,6 @@ pub fn getsockopt<T: Copy>(sock: &Socket, level: c_int, option_name: c_int) -> i
             &mut option_value as *mut T as *mut _,
             &mut option_len,
         ))?;
-        assert_eq!(option_len as usize, mem::size_of::<T>());
         Ok(option_value)
     }
 }