zabbix-agent doesn't exist anymore since 3.0

'-f' option (foreground) is now in zabbix-agentd

003-change-user-and-foreground.patch fixes pending
issue https://support.zabbix.com/browse/ZBX-10611

you might need to update your config file to add
LogType=system

Signed-off-by: Etienne CHAMPETIER <champetier.etienne@gmail.com>

Under musl a compilation unit cannot include both linux/kernel.h
and sys/sysinfo.h at the same time since that leads to a redefinition
of `struct sysinfo`.

Change the autoconf template to include linux/kernel.h while testing
for sys/sysinfo.h to test for that conflict.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>