Fixed typos in Section 4

- Duplicate IP addresses were used for R1 to R4 link and R2 to R3 #1
link.  Also, had to renumber the other links to avoid creating more
duplicated.
- Fixed link IP addresses in ERO's in Sections 4.3 & 4.4.
- Fixed minor typos in other Sections.
Merge pull request #2 from samante/typos_section4

Fixed typos in Section 4