Check out the following article and listing (linked within the article) - the listing is the script they use to set up NIM, but the part you want is the following:
###############################################################################
##
## Subroutine: Set hardware parameters
##
################################################################################
set_hardware ()
{
print "============================"
print "SETUP HARDWARE PARAMETERS "
print "============================"
print ""
for I in `/etc/lsdev -Cc adapter -t 23100020 | /usr/bin/grep Available | awk '{print $1}'`
do
display_info "Set 100 full duplex mode on $I" "chdev -l $I -atx_que_size=2048 -arxbuf_pool_size=2048 -a media_speed='100_Full_Duplex' -P"
done
Here is the link to
Sysadmin article
After checking it out, double check the man page for the chdev command.