kernel: do not strip /proc/net/ip_mr_* in the /proc debloat patch, it is used by iproute2

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt@36529 3c298f89-4303-0410-b956-a3cf2f4a3e73