sysctl net: Keep tcp_syn_retries inside the boundary

[ Upstream commit 651e92716aaae60fc41b9652f54cb6803896e0da ]

Limit the min/max value passed to the
/proc/sys/net/ipv4/tcp_syn_retries.

Signed-off-by: Michal Tesar <mtesar@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>