libhealthloop: Handle netlink receive buffer overflows

The Linux kernel netlink implementation sets EPOLLERR if delivery of a
netlink message fails because of a buffer overrun (see also the Linux
kernel netlink_overrun() and sock_def_error_report() functions). Handle
buffer overruns by calling ScheduleBatteryUpdate() unconditionally.

Bug: 203462310
Change-Id: I54f7d239e6b4caad0db4d1b15de7c0385f796ebd
Signed-off-by: Bart Van Assche <bvanassche@google.com>