The -L command line option was added to the dhcpcd call in the -current
development cycle to assist ARM users with getting networking up and running.
This addition was incorrect as rc.inet1 already has support to use or not use
-L by setting DHCP_NOIPV4LL[x]="".  When I was updating rc.inet1 I took out
the -L, but didn't make it clear enough why I had taken it out and how to use
the DHCP_NOIP4ALL[x]="" option in rc.inet1.conf.  This commit is simply
updating that comment to be more verbose.

The rest of the shellcheck issues are non-issue warnings that
could possibly do with being corrected, but it's not a huge issue.

Thanks to Fraks on LQ.

Thanks to Master-Passeli for the bug report.

A lot of the changes are formatting (I had a bug I couldn't hunt down and the
formatting wasn't helping), but there's quite a few new dialogs - not only
to configure IPv6, but adding better user input issue handling.

* Modify creation of the rc.inet1.conf file to incorporate IPv6.
* Edited error text in syntax_check_color() to be more generic.
* Added SLAAC option to the configuration type menu.
* Added a new DHCP selection menu to cater for v4, v6 and both configurations.
* Edited various dialog texts to be more consistent and/or IPv6 friendly.
* Validate netmask that's entered by the user.
* Produce an error about missing netmask when IPv4 IP is set.
* Only do netmask and gateway (IPv4) prompting if an IPv4 address was set.
* Added static IPv6 configuration dialogs.
* Updated nameserver configuration dialog.
* Added IPv6 fields to the final static IP confirmation/edit screen.