BB: brcm63xx: uci-defaults: network: move DSL-274x1 F1 to right section

The cpu port is at 8, not 5.

Fixes #18406.

Backport of r43379.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/branches/barrier_breaker@43380 3c298f89-4303-0410-b956-a3cf2f4a3e73