network: avoid including sys/sysctl.h on Linux

The sys/sysctl.h header is only needed on BSD platforms to get
the sysctlbyname() function declaration. On Linux we talk to
procfs instead to change sysctls.

Unfortunately a legacy sys/sysctl.h header does exist on Linux
and including it has recently started triggering a deprecation
warning from glibc.

Protect its inclusion with a HAVE_SYSCTLBYNAME check instead
so that it only gets used on platforms where we need that
function declaration.
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

src/network/bridge_driver.c

@@ -33,7 +33,7 @@
 #include <sys/wait.h>
 #include <sys/ioctl.h>
 #include <net/if.h>
-#if HAVE_SYS_SYSCTL_H
+#ifdef HAVE_SYSCTLBYNAME
 # include <sys/sysctl.h>
 #endif