allow retries of if_config

[bendmorris]

Currently if you call if_config and it returns an error subsequent calls will immediately return 0 and won't repeat any initialization that failed.

This change keeps track of what's been initialized so that initialization can be resumed.

[WinterMute]

How often are you seeing failures and at what point does it usually fail?

[bendmorris]

I was seeing failure with -1 when the bba wasn't connected to anything, as you might expect. Would be nice to be able to warn and retry in that case.

[WinterMute]

That'll do it :P

How far in the intialisation does it get without a cable?

[bendmorris]

Didn't check, but from the return I guess it either failed on MQ_Init or netif_add.