misc/53153: Fix rump build in DragonFlyBSD

[tuxillo%quantumachine.net@localhost]

>Number:         53153
>Category:       misc
>Synopsis:       Fix rump build in DragonFlyBSD
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    misc-bug-people
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Tue Apr 03 23:35:00 +0000 2018
>Originator:     Antonio Huete Jimenez
>Release:        latest source
>Organization:
DragonFlyBSD
>Environment:
>Description:
DragonFly defaults to -Werror so a missing include causes rump to fail to build (via buildrump)

The patch below allows the build to finish. It should be no problem to include unistd.h unconditionally but if needed I can change it to be included only in the dragonfly case.
>How-To-Repeat:

>Fix:
diff --git a/sys/rump/net/lib/libshmif/shmif_user.c b/sys/rump/net/lib/libshmif/shmif_user.c
index 70c64ab6..05c8e5f1 100644
--- a/sys/rump/net/lib/libshmif/shmif_user.c
+++ b/sys/rump/net/lib/libshmif/shmif_user.c
@@ -47,6 +47,7 @@
 #include <sys/event.h>
 
 #include <stdlib.h>
+#include <unistd.h>
 
 int
 rumpcomp_shmif_watchsetup(int *kqp, int fd)