strongswan: move uci-defaults migration into subfunction

To make the migration script more organized, the migration for the 'ipsec'
unamed section to 'ipsec' named section 'globals' has been moved to a
subfunction.

The change prepares the new migration script to migrate other areas.

Signed-off-by: Florian Eckert <fe@dev.tdt.de>

net/strongswan/files/etc/uci-defaults/strongswan

@@ -1,6 +1,6 @@
 #!/bin/sh
 
-main() {
+migrate_ipsec() {
 	# Skip migration if the 'globals' section already exists
 	uci show ipsec.globals 1>/dev/null 2>/dev/null
 	[ "$?" = "0" ] && return
@@ -10,6 +10,10 @@ main() {
 	uci -q commit ipsec
 }
 
+main() {
+	migrate_ipsec
+}
+
 main
 
 exit 0