[TYPO] document and cli helper typo

Hello,

We found there is some typos in cli and document like "<acl INDEX>" instead of "acl <INDEX>"
[un]Apply an ACL to an interface: 
[plugins/acl/acl.c:L3756](https://github.com/FDio/vpp/blob/master/src/plugins/acl/acl.c#L3756)
[un]Apply a MACIP ACL to an interface: 
[plugins/acl/acl.c:L3817](https://github.com/FDio/vpp/blob/master/src/plugins/acl/acl.c#L3817)
