isisd: fix point-to-point network type config

isisd: fix point-to-point network type config

`isis network point-to-point` was being rejected from the configuration
file as it was being processed before the reception of the UP zebra
notification for the interface. This meant that the `circ_type` was set
at CIRCUIT_T_UNKNOWN, which led the northbound callback to fail. This
check was removed as it was not really necessary; when the zebra
notification is received, the correct circuit type will be enforced,
but now the point-to-point config will be saved and correctly applied
when zebra recognizes the interface as a broadcast one.

Signed-off-by: Emanuele Di Pascale <emanuele@voltanet.io>