net.ipv4.tcp_tw_recycle has been removed from Linux 4.12 but, still,
makes sense to check its existence. Unfortunately, current check does
not test for the procfs file existence. This commit fixes the issue.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13984



Signed-off-by: Rafael David Tinoco <rafaeldtinoco@ubuntu.com>
Reviewed-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>

Autobuild-User(master): Andreas Schneider <asn@cryptomilk.org>
Autobuild-Date(master): Tue Jun  4 23:31:24 UTC 2019 on sn-devel-184

(cherry picked from commit 843fbb12)