BUG/MINOR: spoe: Be sure to set tv_request when each message fragment is encoded

When a message or a fragment is encoded, the date the frame processing starts
must be set if it is undefined. The test on tv_request field was wrong.

This patch must be backported to 1.9.
diff --git a/src/flt_spoe.c b/src/flt_spoe.c
index 703d6ba..1b51779 100644
--- a/src/flt_spoe.c
+++ b/src/flt_spoe.c
@@ -2674,8 +2674,8 @@
 	}
 
 	if (ctx->state == SPOE_CTX_ST_ENCODING_MSGS) {
-		if (!tv_iszero(&ctx->stats.tv_request))
-		    ctx->stats.tv_request = now;
+		if (tv_iszero(&ctx->stats.tv_request))
+			ctx->stats.tv_request = now;
 		if (!spoe_acquire_buffer(&ctx->buffer, &ctx->buffer_wait))
 			goto out;
 		ret = spoe_encode_messages(s, ctx, messages, dir, type);