selftests: net: modify IOAM tests for undef bits

The output behavior for undefined bits is now directly tested inside the bash
script. Trying to set an undefined bit should be refused.

The input behavior for undefined bits has been removed due to the fact that we
would need another sender allowed to set undefined bits.

Signed-off-by: Justin Iurman <justin.iurman@uliege.be>
Signed-off-by: David S. Miller <davem@davemloft.net>