Include what you use: <unistd.h>

This was transitively included, but no longer is, so it must be
explicitly included.

Test: build
Bug: 157822244
Change-Id: Ifa85582c9380df6f16025eba86b64e9af32bc226
Merged-In: Ifa85582c9380df6f16025eba86b64e9af32bc226
diff --git a/server/NetlinkManager.cpp b/server/NetlinkManager.cpp
index d014443..e3c1db9 100644
--- a/server/NetlinkManager.cpp
+++ b/server/NetlinkManager.cpp
@@ -17,6 +17,7 @@
 #include <errno.h>
 #include <stdio.h>
 #include <string.h>
+#include <unistd.h>
 
 #include <sys/socket.h>
 #include <sys/time.h>