acl-plugin: acl-as-a-service: VPP-1248: fix the error if exports.h included in more...

acl-plugin: acl-as-a-service: VPP-1248: fix the error if exports.h included in more than one C file

Including the exports.h from multiple .c files belonging to a single plugin results in an error.

Rework the approach to require the table of function pointers to be filled in by
the initialization function.

Since the inline functions are compiled in the "caller" context,
there is no knowledge about the acl_main structure used by the ACL
plugin. To help with that, the signature of inline functions is slightly
different, taking the p_acl_main pointer as the first parameter.

That pointer is filled into the .p_acl_main field of the method
table during the initialization - since the calling of non-inline variants
would have required filling the method table, this should give
minimal headaches during the use and switch between the two methods.

Change-Id: Icb70695efa23579c46c716944838766cebc8573e
Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>