include: calculate md5sum over sorted kernel config symbol list and incorperate it...

include: calculate md5sum over sorted kernel config symbol list and incorperate it into the kernel metapackage version, make kmods depend on this specific version.
The aim of this change is to invalidate kmods which are built against a different kernel config on the opkg metadata level. Manual copying and insmod of custom
*.ko files, e.g. for development purpose, is still possible.

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@29686 3c298f89-4303-0410-b956-a3cf2f4a3e73