ipblocklist-functions.pl: Specify an IPFire user agent for the downloads

ipblocklist-functions.pl: Specify an IPFire user agent for the downloads

- As discussed at the IPFire conf call in March 2025, this patch provides an IPFire
   specific User Agent string for the IP Block Lists downloads using LWP::UserAgent.
- It turned out that there was already a function in general-functions.pl that creates
   an IPFire Useer Agent string. This was used for this IP Blocklist download.
- Currently it gave me the string IPFire/2.29/192.
- This was tested out with the Threatview.io IP blocklist download and it worked fine.
- If this patch is approved and merged then I will let contact Threatview.io to let them
   know what our User Agent string is.

Tested-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>