Revise SDL 0317 - SDL Protocol Security Specification

[dboltovskyi]

Revised proposal based on review comments (see https://github.com/smartdevicelink/sdl_evolution/issues/1070#issuecomment-857760129)

Updates

• Updated section "Change 1: Update Frame Header Fields description": Removed changes related to "Frame Info"
• Updated section "4.2.5 Start Service": Added section number for "Secured Communication"
• Updated section "7. Secured Communication": Added details on re-starting of service
• Updated section "Impact on existing code": Removed any impact except "Protocol specification"
• Updated section "Impacted Platforms": Removed everything except "Protocol"

[dboltovskyi]

@theresalech Please notice PR is ready for PM review.

[dboltovskyi]

@theresalech Thank you for your review. Suggested change is applied in 244f788c4084767f1b4ea962ee8ce41f221cd836