Update LNW + IPsec documentation for 1.8

[5abeel]

Changes in this PR

• Updated all load_custom_config.sh to make it generic, with a comment to indicate two fields are for LAG and IPsec usecase
• Update the IPsec doc to point that we now use the LNW combined recipe
• Remove the second half of the IPsec doc which simply gives some design details -- something that the user does not have to handle manually. All this is done by the ipsec strongSwan plugin code
• LAG/LACP has seen some issues when bulk programming rules -- adding a delay avoids this problem. Added a note in documentation to point this out

[ffoulkes]

Note corrections.

Otherwise, LGTM.