test_exec: SO_KEEPALIVE value only needs to be true (take #2)

We need to ensure the portability of the sd_listen_fds emulation
test, too, which didn't get tested on my FreeBSD 10.3 install
due to it being on Ruby 2.2

Followup-to: 4ce6b00 ("test_exec: SO_KEEPALIVE value only needs to be true")

Author: Eric Wong

test/exec/test_exec.rb

@@ -122,7 +122,7 @@ def test_sd_listen_fds_emulation
       res = hit(["http://#@addr:#@port/"])
       assert_equal [ "HI\n" ], res
       assert_shutdown(pid)
-      assert_equal 1, sock.getsockopt(:SOL_SOCKET, :SO_KEEPALIVE).int,
+      assert sock.getsockopt(:SOL_SOCKET, :SO_KEEPALIVE).bool,
                   'unicorn should always set SO_KEEPALIVE on inherited sockets'
     end
   ensure