Update draft-psenak-ospf-segment-routing-extensions.xml

- added one more paragraph related to E and P bits in Prefix-SID sub-TLV
- fixed the length field in Prefix-SID subTLV
- Added reserved range to TLVs and sub-TLVs inside Extended Prefix/Link LSAs
- moved the Reserved field next to Flags in Adj-SID and LAN Adj-SID sub-TLVs for consistency