pbr: update to 1.1.7-7

pbr: update to 1.1.7-7

Makefile:
* remove pbr-iptables flavour

Init-script:
* improve detection of wireguard server and client instances
* integrate wg_server_and_client into init script
* remove traffic_killswitch() and trap() and related options/code
* remove internal nft_file_support variable as fw4 nft file is the only running mode
* improve debug() and is_supported_interface() functions
* improve detection of incompatible user script files
* double-quote some strings due to shellcheck errors
* flush ip rules from pbr tables instead of deleting last one

Other files:
* remove /usr/share/pbr/pbr.user.wg_server_and_client as obsolete
* remove references to the file above in config on update thru uci-defaults
* minor updates to netifd uci-defaults script

Signed-off-by: Stan Grishin <redacted>