network:dhcp4_server_configure returns if not able to get timezone

network:dhcp4_server_configure returns if not able to get timezone

When /etc/localtime is a symbolic link pointing to another symbolic
link, get_timezone will return -EINVAL instead of the timezone.
This issue can cause systemd-networkd DHCPServer to fail.

Instead of returning failure, log a warning indicating that that
the timezone will not be sent.

	modified:   networkd-dhcp-server.c

(cherry picked from commit 7b5018ca9e6d3279887ec7113818f41d5b831c4d)
(cherry picked from commit 37c4cfde0ce613f0f00544d3f4e2e72bf93d9c76)
(cherry picked from commit db85ea172f9b4e6cd2f46bffd63164a09404001f)