[packages] olsrd: init: for better reuse, make a function out of a procedure get_valu...

[packages] olsrd: init: for better reuse, make a function out of a procedure get_value_for_entry()

Later we want to reuse that functionality, to avoid code duplication
we make a function with clean entry and return-codes, so we can do e.g.:

get_value_for_entry "$entry" || continue

which is also better readable.

Signed-off-by: Bastian Bittorf <bittorf@bluebottle.com>
git-svn-id: svn://svn.openwrt.org/openwrt/packages@36298 3c298f89-4303-0410-b956-a3cf2f4a3e73