[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@36298 3c298f89-4303-0410-b956-a3cf2f4a3e73
[packages] olsrd: init: parse new var 'speed', which translates to several other vars

Range is 1...20 where 1 is fastest protocol speed and 20 is the slowest protocol speed

Like in the Freifunk-Firmware from sven-ola we accept now a per-interface
option 'speed', which should range from 1...20 and is sanitized. when the
value is not in valid range, it defaults to 6 which allows the daemon to
start and behave like in a city-wide mesh. (same default like in freifunk firmware)

The value 'speed' overrides the normal values for emission intervals like
Hello-, Tc-, Mid-, Hna-Interval/ValidityTime or sets them explicitely. this
makes it much easier to play with intervals on several routers:

Instead of changes eight values, we only have to alter 1 value.

The value-calculation is tested since several years.

Signed-off-by: Bastian Bittorf <bittorf@bluebottle.com>

git-svn-id: svn://svn.openwrt.org/openwrt@36299 3c298f89-4303-0410-b956-a3cf2f4a3e73
[packages] olsrd: init: reduce code duplication by reusing already_in_schema()

changed scope/position of this function, and reuse it.

Signed-off-by: Bastian Bittorf <bittorf@bluebottle.com>

git-svn-id: svn://svn.openwrt.org/openwrt@36300 3c298f89-4303-0410-b956-a3cf2f4a3e73