Needs a bit of observation, but as far as I can see the only difference
is that is_numeric() will also take int values and return true for them,
ctype_digit() will only return true for string values that have digits.

Taken from: http://www.iana.org/assignments/icmp-parameters/icmp-parameters.xhtml

This makes it easier to migrate cron jobs in the future.  Still not
all callers converted, but we'll get there.  ;)

Suggested by: @fabianfrz

(traffic shaper) add advanced option schedule type for pipe, makes current default (wf2q+) explicit. related to https://github.com/opnsense/core/issues/505