xdf_add_channel() appends a channel to the file referenced by the handle xdf. The new channel is
initialized with the label argument (if not NULL) and with the default channel values set in the XDF
file, i.e. those set using channel configuration fields in xdf_set_conf(3) (See the related manpage).
If the call to xdf_add_channel(3) is successful, the default offset value (the field referenced by
XDF_CF_ARROFFSET) is incremented by the size of the current default stored type (field referenced by
XDF_CF_STOTYPE). As a consequence, if the channel default values have not changed in-between, the next
call to xdf_add_channel() will create a channel whose location is the array will be next to the previous
one.
This type of initialization allows the user to add channels without having to specifically pack them:
this is achieved by default.