acl-plugin: change the src/dst L3 info in 5tuple struct to be always contiguous with...

Using ip46_address_t was convenient from operational point of view but created
some difficulties dealing with IPv4 addresses - the extra 3x of u32 padding
are costly, and the "holes" mean we can not use the smaller key-value
data structures for the lookup.

This commit changes the 5tuple layout for the IPv4 case, such that
the src/dst addresses directly precede the L4 information.
That will allow to treat the same data within 40x8 key-value
structure as a 16x8 key-value structure starting with 24 byte offset.

Change-Id: Ifea8d266ca0b9c931d44440bf6dc62446c1a83ec
Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>