check gateway for IPv6 also for reply-to rules.
add gre and gif checks for for IPv4 function interface_has_gateway($friendly), like they are already for IPv6
Load if_stf module when needed
Merge pull request #1115 from PiBa-NL/reply-to_IPv6gateway
Merge pull request #1116 from PiBa-NL/interface_has_gateway-ipv4_gif_gre
Fix PBI symlink creation and deletion under /usr/local following .pbiopt files, also drop setup_library_paths() since it's not necessary anymore
Missed pbi_prefix here