use threads;
use Net::SSH2;

async {
    my $ssh = Net::SSH2->new( ... );
    $ssh->scp_put($firmware[$antenna_type],'/tmp/fwupdate.bin');
    print "Upgrading firmware, this will take about 3 minutes.\n";
    my $chan = $ssh->channel();
    $chan->exec("/sbin/fwupdate -m\n");
    $chan->close;
}->detach;

...