wireguard-tools: fix script errors

wireguard-tools: fix script errors

follow-up to 148207730a3c9f3aea807df336ca33792e9d3c0f

Schoolboy error on the peer_psk value.

Also fix an issue when joining peer IPv4 and IPv6 AllowedIPs
(${peer_a_ips/ /, } replaces only the first space, while
${peer_a_ips// /, } replaces all the spaces).

Closes: https://github.com/openwrt/openwrt/issues/21847
Signed-off-by: Paul Donald <newtwen+github@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/21851
Signed-off-by: Robert Marko <robimarko@gmail.com>