* Simplify EINTR/ECANCEL error handling
1. Add semaphore uninterruptible wait function
2 .Replace semaphore wait loop with a single uninterruptible wait
3. Replace all sem_xxx to nxsem_xxx
* Unify the void cast usage
1. Remove void cast for function because many place ignore the returned value witout cast
2. Replace void cast for variable with UNUSED macro
There are two issues with it however:
1. Reading from file system on a per packet basis could be slow. I think it probably should have a small, in-memory cache of most frequently used routes for good problem.
2. Currently the delroute logic is disabled due to a problem with the design. NuttX does not currently support truncate(). Therefore, it is not possible to delete entries from the routing table file.
In this current implementation, that leaves the last entry intact at the end of the file. An alternative design might include a tag on each record to indicate if the record is valid or not. That would work but would add complexity to the other routing table functions.
The existing implementation is available for testing purposes only if CONFIG_EXPERIMENTAL=y.
Squashed commit of the following:
net/route: The current delroute design depends on file truncation. However, NuttX does not currently support truncate. Alternative, more complex designs are possible but not implemented. At present the file routing table are otherwise functional but the delroute logic is disabled via CONFIG_EXPERIMENTAL. Enable it only if you plan to fix it.
net/route: Fix some issues with locking routing table files.
net/route: Add partial implementation of delroute for the case where the routing table is in a file.
net/route: Add support for seeking to positions in the routing table.
net/route: Add net_addroute_ipv4/6() using a file-based routing table.
net/route: Add net_foreach_ipv4/4() using a file-based routing table.
net/route: Initial build, configuration, and fs utilies to support routing tables in a file.
