keepalive swap interval and probes

The interval and probes members for setting keepalive options
per-connection on Linux were swapped.

Signed-off-by: Larry Hayes <lhayesg@gmail.com>
diff --git a/lib/libwebsockets.c b/lib/libwebsockets.c
index 8756de7..a4d352c 100644
--- a/lib/libwebsockets.c
+++ b/lib/libwebsockets.c
@@ -578,12 +578,12 @@
 					     (const void *)&optval, optlen) < 0)
 			return 1;
 
-		optval = context->ka_probes;
+		optval = context->ka_interval;
 		if (setsockopt(fd, IPPROTO_IP, TCP_KEEPINTVL,
 					     (const void *)&optval, optlen) < 0)
 			return 1;
 
-		optval = context->ka_interval;
+		optval = context->ka_probes;
 		if (setsockopt(fd, IPPROTO_IP, TCP_KEEPCNT,
 					     (const void *)&optval, optlen) < 0)
 			return 1;