Random INVs if we connect to regtest after connecting to testnet previously

[Varunram]

I first dismissed these as coincidences, but apparently they're not since I've observed this for quite sometime now. How it works is you've to be connected to testnet for a while and then when you switch to regtest, you may be able to reproduce this bug.

2018/06/21 00:36:22.883208 got inv.  Contains:
2018/06/21 00:36:22.883231 	0)MSG_BLOCK : 39583b96111282554e2db6e1e9aca8637e85002b288ee70231c043a85983371e
2018/06/21 00:36:22.883239 inv block but ignoring; not synced
2018/06/21 00:47:34.079141 got inv.  Contains:
2018/06/21 00:47:34.079254 	0)MSG_BLOCK : 5d672c47a4beb7eb641f8c94d8881be8b353a943f20ef35514b5d0367cc4a0d7
2018/06/21 00:47:34.079276 inv block but ignoring; not synced
2018/06/21 00:47:40.664307 got inv.  Contains:
2018/06/21 00:47:40.664326 	0)MSG_BLOCK : 2820ab1843eff0ff24935a4f49fb6a954e5f2f146b563002ca966409f692017b

[delbonis]

I think this might just be a side effect of how regtest works. I replicated the behavior but I think that it might just be doing that because of something to do with how there's no time checks on the block generation on regtest.