Extend the nwfilter.rng schema to accept state attribute.

Extend the nwfilter.rng schema to accept comment attributes for all protocol
types.

This patch adds an optional XML attribute to a nwfilter rule to give the user control over whether the rule is supposed to be using the iptables state match or not. A rule may now look like shown in the XML below with the statematch attribute either having value '0' or 'false' (case-insensitive).

[...]
<rule action='accept' direction='in' statematch='false'>
<tcp srcmacaddr='1:2:3:4:5:6'
           srcipaddr='10.1.2.3' srcipmask='32'
           dscp='33'
           srcportstart='20' srcportend='21'
           dstportstart='100' dstportend='1111'/>
</rule>
[...]

I am also extending the nwfilter schema and add this attribute to a test case.

So far the references to other filters needed to appear before filtering
rules. With the below patch they can now appear in any order.

Also I forgot to add a couple of 'rarp's.

This patch adds support for the RARP protocol. This may be needed due to
qemu sending out a RARP packet (at least that's what it seems to want to
do even though the protocol id is wrong) when migration finishes and
we'd need a rule to let the packets pass.

Unfortunately my installation of ebtables does not understand -p RARP
and also seems to otherwise depend on strings in /etc/ethertype
translated to protocol identifiers. Therefore I need to pass -p 0x8035
for RARP. To generally get rid of the dependency of that file I switch
all so far supported protocols to use their protocol identifier in the
-p parameter rather than the string.

I am also extending the schema and added a test case.

changes from v1 to v2:
- added test case into patch

With this patch I want to enable hex number inputs in the filter XML. A
number that was entered as hex is also printed as hex unless a string
representing the meaning can be found.

I am also extending the schema and adding a test case. A problem with
the DSCP value is fixed on the way as well.

Changes from V1 to V2:

- using asHex boolean in all printf type of functions to select the
output format in hex or decimal format

I am extending the schema with the recently added connlimit-above
attribute and adding a test case for it to the test suite.

Fixing the regular expressions for variables where the first letter must be a $.

This patch adds a relaxng nwfilter schema along with a test that
verifies all the test output XML against the schema. The input XMLs
contain a lot of intentional out-of-range values that make them fail the
schema verification, so I am not verifying against those.