netifd: propagate error code on netifd_reload()

netifd: propagate error code on netifd_reload()

The context is that we generate some of the UCI config
for netifd via scripts/programs.

Every once in a while, there's a goof when doing that
UCI generation, and netifd prints out the error at
stderr, but returns 0 (success) err-code.

This change will fail the ubus call if UCI config
is invalid or missing for /etc/config/network.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>
Acked-by: Hans Dedecker  <dedeckeh@gmail.com>