When compiled with musl >1.1.20, fastd will crash in case it can't
resolve a peers hostname. This is due to a changed implementation of
freeaddrinfo in musl 1.1.21 onwards.

This segfault is fixed by not calling freeaddrinfo in case the supplied
pointer is null.

Signed-off-by: David Bauer <mail@david-bauer.net>

Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>

Prefer linux/if_ether.h over netinet/if_ether.h if available since the
musl libc if_ether.h header does not allow mixing with kernel headers,
it will result in a struct ethhdr redefinition error.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>
Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>