net: fill in MODULE_DESCRIPTION()s for xen-netback

W=1 builds now warn if module is built without a MODULE_DESCRIPTION().
Add descriptions to the Xen backend network module.
Signed-off-by: Breno Leitao <leitao@debian.org>
Acked-by: Paul Durrant <paul@xen.org>
Link: https://lore.kernel.org/r/20240214152741.670178-2-leitao@debian.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/xen-netback/netback.c

@@ -1778,5 +1778,6 @@ static void __exit netback_fini(void)
 }
 module_exit(netback_fini);
 
+MODULE_DESCRIPTION("Xen backend network device module");
 MODULE_LICENSE("Dual BSD/GPL");
 MODULE_ALIAS("xen-backend:vif");