First stab at integrating the acl-plugin from VPP. Allow to craft ACLs
consisting of one-or-more ACEs (this is ensured by 'terms' being
required with min=1), and a rich language to be able to set any L3
and L4 (UDP, ICMP, TCP) matchers that the plugin provides.
Explain how the syntax will look like, although for now only YAMALE
syntax checking can be performed (semantic validation is next).
TESTED:
pim@hippo:~/src/vppcfg/vppcfg$ ./vppcfg.py check -c example.yaml
[INFO ] root.main: Loading configfile example.yaml
[INFO ] vppcfg.config.valid_config: Configuration validated successfully
[INFO ] root.main: Configuration is valid
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