* gprs_ns2_sns: move gss->remote specific check out of add_ip4_elem/add_ip6_elem
* gprs_ns2_sns: use struct ns2_sns_elems in add/update/remove remote_elems
* gprs_ns2_sns: refactor ns2_clear_ipv46_entries_local to use new elems functions
* gprs_ns2_sns: refactor local and remote entries into a struct
* gprs_ns2_sns: bss: improve validation of configuration
* gprs_ns2_sns: move selection of the next bind into own function