use function stats_reset_interval()

use function stats_reset_interval()

Git commit bb8d71ef27f673f25c7e1648ea982c27bb61ac0d from 2020 among many
other things introduced the function stats_reset_interval() to reset the
*_i interval (or split) host statistics, but did not use it.  This commit
replaces the open coded reset of interval stats inside print_host_splits()
and print_netdata() with calling stats_reset_interval().