iproute2: update to version 6.18

iproute2: update to version 6.18

The removed patch 001-lib-bridge-avoid-redefinition-of-in6_addr.patch
was integrated upstream.

Changes: https://github.com/iproute2/iproute2/compare/v6.17.0...v6.18.0

The apk size did not increase much:
Old size for armsr/armv8:
 43778 ip-bridge-6.17.0-r1.apk
164653 ip-tiny-6.17.0-r1.apk
208236 tc-bpf-6.17.0-r1.apk
210209 tc-full-6.17.0-r1.apk
172483 tc-tiny-6.17.0-r1.apk

new size for armsr/armv8:
 43781 ip-bridge-6.18.0-r1.apk
164956 ip-tiny-6.18.0-r1.apk
208578 tc-bpf-6.18.0-r1.apk
210482 tc-full-6.18.0-r1.apk
172664 tc-tiny-6.18.0-r1.apk

Link: https://github.com/openwrt/openwrt/pull/21101
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>