Fix for issue #2765 relative to unstable trafficshaping test procedure

Motivation:

The test procedure is unstable due to not enough precise timestamping
during the check.

Modifications:

Reducing the test cases and cibling "stable" test ("timestamp-able")
bring more stability to the tests.

Result:

Tests for TrafficShapingHandler seem more stable (whatever using JVM 6,
7 or 8).
Fix checkstyle
[maven-release-plugin] prepare release netty-4.1.0.Beta3
[maven-release-plugin] prepare for next development iteration
Better fix for TrafficShapingHandlerTest

Motivation:
It seems that in certain conditions, the write back from the server is so quick that the handler has no time to compute traffic shaping. So 10ms of wait before acknowledging is added in server side.

Modifications:
Add 10ms waiting before server ackonwledge the client.

Result:
The timing is now suppsed to be stable.
Better fix for TrafficShapingHandlerTest

Motivation:
The test procedure is unstable when testing quick time (factor less or equal to 1). Changing to default 10ms in this case will force time to be correct and time to be checked only when factor is >= 2.

Modifications:
When factor is <= 1, minimalWaitBetween is 10ms

Result:
Hoping this version is finally stable.
Support IPv4 default route in ipfilter.

Motivation:

In GitHub issue #2767 a bug was reported that the IPv4
default route leads to the ipfilter package denying
instead of accepting all addresses.

While the issue was reported for Netty 3.9, this bug
also applies to Netty 4 and higher.

Modifications:

When computing the subnet address from the CIDR prefix,
correctly handle the case where the prefix is set to zero.

Result:

Ipfilter accepts all addresses when passed the
IPv4 default route.