interfaces: remove the "Directly send SOLICIT" option

We already do a more-or-less hybrid approach by starting rtsold
even if it isn't used at all.  Now we also have ISPs which do
not seem to send router advertisements after successful connect
so that the reconnect misses the HUP for dhcp6c to fix the
connectivity again.

To change that remove the option and its only conditional to
behave unconditionally which has few reasons to cause regressions.

src/etc/inc/interfaces.inc

@@ -2938,9 +2938,8 @@ function interface_dhcpv6_configure($interface = 'wan', $wancfg)
         )
     );
 
-    if (isset($wancfg['dhcp6sendsolicit'])) {
-        mwexec("/var/etc/rtsold_{$realifv6}_script.sh");
-    }
+    /* unconditional trigger for hybrid approach, reloads without advertisements */
+    mwexec("/var/etc/rtsold_{$realifv6}_script.sh");
 }
 
 function interface_dhcpv6_prepare($interface = 'wan', $wancfg)

src/www/interfaces.php

@@ -437,7 +437,6 @@ function get_wireless_channel_info($interface) {
     $pconfig['blockbogons'] = isset($a_interfaces[$if]['blockbogons']);
     $pconfig['dhcpoverridemtu'] = empty($a_interfaces[$if]['dhcphonourmtu']) ? true : null;
     $pconfig['dhcp6-ia-pd-send-hint'] = isset($a_interfaces[$if]['dhcp6-ia-pd-send-hint']);
-    $pconfig['dhcp6sendsolicit'] = isset($a_interfaces[$if]['dhcp6sendsolicit']);
     $pconfig['dhcp6prefixonly'] = isset($a_interfaces[$if]['dhcp6prefixonly']);
     $pconfig['dhcp6usev4iface'] = isset($a_interfaces[$if]['dhcp6usev4iface']);
     $pconfig['dhcp6norelease'] = isset($a_interfaces[$if]['dhcp6norelease']);
@@ -1176,9 +1175,6 @@ interface_sync_wireless_clones($a_interfaces[$if], false);
                     if (!empty($pconfig['dhcp6prefixonly'])) {
                         $new_config['dhcp6prefixonly'] = true;
                     }
-                    if (!empty($pconfig['dhcp6sendsolicit'])) {
-                        $new_config['dhcp6sendsolicit'] = true;
-                    }
                     if (!empty($pconfig['dhcp6usev4iface'])) {
                         $new_config['dhcp6usev4iface'] = true;
                     }
@@ -2734,15 +2730,6 @@ function toggle_allcfg() {
                             </div>
                           </td>
                         </tr>
-                        <tr>
-                          <td><a id="help_for_dhcp6sendsolicit" href="#" class="showhelp"><i class="fa fa-info-circle"></i></a> <?=gettext('Directly send SOLICIT'); ?></td>
-                          <td>
-                            <input name="dhcp6sendsolicit" type="checkbox" id="dhcp6sendsolicit" value="yes" <?= !empty($pconfig['dhcp6sendsolicit']) ? 'checked="checked"' : '' ?>/>
-                            <div class="hidden" data-for="help_for_dhcp6sendsolicit">
-                              <?= gettext('In case the ISP requires a SOLICIT message for authentication, select this option to prevent indefinite waiting for a router advertisement.') ?>
-                            </div>
-                          </td>
-                        </tr>
                         <tr>
                           <td><a id="help_for_dhcp6norelease" href="#" class="showhelp"><i class="fa fa-info-circle"></i></a> <?=gettext("Prevent release"); ?></td>
                           <td>