[GH-28396] Fixed errcheck issues in server/channels/api4/ip_filtering.go (#28441)

* Fixed errcheck issues in server/channels/api4/ip_filtering.go

* Added separate go routine to SendIPFiltersChangedEmail and removed redundant return

* Added import for mlog

* Changed from returning error to logging it

---------

Co-authored-by: Ben Schumacher <ben.schumacher@mattermost.com>

server/.golangci.yml

@@ -82,7 +82,6 @@ issues:
         channels/api4/handlers_test.go|\
         channels/api4/import_test.go|\
         channels/api4/integration_action_test.go|\
-        channels/api4/ip_filtering.go|\
         channels/api4/ip_filtering_test.go|\
         channels/api4/job_test.go|\
         channels/api4/license.go|\