This function appends the transmission matrix created during
infection.net and infection.2g.net.
set_transmat(dat, del, at)The updated dat main list object.
Main list object containing a networkDynamic object and
other initialization information passed from netsim.
Discordant edgelist created within infection.net and
infection.2g.net.
Current time step.
This internal function works within the parent infection.net
functions to save the transmission matrix created at time step at to
the main list object dat.