Fix network opcode parameters

Commit 32e3d8b1 (“opcodes: Network parameter improvements and fixes”)
changed a few parameters in the network add, connect and set params
opcodes, but some of the changes are buggy. The patch changed the type
to TMaybe(), whereas the default should have been changed from None to
NoDefault - the network, mode and link are required. It also wrongly
unified all types as _CheckCIDRNetNotation, whereas some are
AddrNotation.

The patch fixes these (correctly, I hope) and also add some new
aliases for readability.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>