Fix console set interface IP address

Problem as per forum https://forum.pfsense.org/index.php?topic=83651.0
The problem comes whenever services_dhcpd_configure is called - the global $config gets reset from the actual current config, and any pending changes in the current process are lost.
It was introduced by commit 86ce2df
in which services_dhcpdv4_configure() does:

require_once('pkg-utils.inc')

and pkg-utils.inc does various stuff like:

if(file_exists("/cf/conf/use_xmlreader"))
require_once("xmlreader.inc");
else
require_once("xmlparse.inc");

which seems to cause a reset of the $config variable, thus losing the pending changes the user has entered at the console.

The top-level code in rc.initial.setlanip really does not need to (and should not) implement any changes along the way - it should collect all the answers from the user, then write_config and then make all the necessary calls to routines to implement the changes on the running system. This fixes it - defer any calls to services_dhcpd_configure() until after all questions are answered and write_config has happened.
Fixup dhcpd interface enabled check
Merge pull request #1329 from phil-davis/patch-3