MINOR: cli: make "show fd" report the fd's thread mask

This is useful to know what thread(s) an fd is scheduled to be
handled on. It's worth noting that at the moment the "show fd"d
doesn't seem totally thread-safe.
diff --git a/src/cli.c b/src/cli.c
index 9c77949..6625a09 100644
--- a/src/cli.c
+++ b/src/cli.c
@@ -825,7 +825,7 @@
 			li = fdt.owner;
 
 		chunk_printf(&trash,
-			     "  %5d : st=0x%02x(R:%c%c%c W:%c%c%c) ev=0x%02x(%c%c%c%c%c) [%c%c%c%c] cache=%u owner=%p iocb=%p(%s)",
+			     "  %5d : st=0x%02x(R:%c%c%c W:%c%c%c) ev=0x%02x(%c%c%c%c%c) [%c%c%c%c] cache=%u owner=%p iocb=%p(%s) tmask=0x%lx",
 			     fd,
 			     fdt.state,
 			     (fdt.state & FD_EV_POLLED_R) ? 'P' : 'p',
@@ -850,7 +850,8 @@
 			     (fdt.iocb == conn_fd_handler)  ? "conn_fd_handler" :
 			     (fdt.iocb == dgram_fd_handler) ? "dgram_fd_handler" :
 			     (fdt.iocb == listener_accept)  ? "listener_accept" :
-			     "unknown");
+			     "unknown",
+			     fdt.thread_mask);
 
 		if (fdt.iocb == conn_fd_handler) {
 			chunk_appendf(&trash, " cflg=0x%08x", conn_flags);