lcbio: Refactor E/C structures into a union

We don't ever use these two structures together and it makes the base
connection object itself smaller as well.

Change-Id: Ia414828372a8a9fde15ab25bc809c325cf50f54b
Reviewed-on: http://review.couchbase.org/33589
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>