bgp: make bfdStatus be lowercase for nonestd sessions

[AndryNick98]

Description

BGP's bfdStatus was not lowercased for Cumulus/EOS when session was not in Estd state. This PR fix it

Type of change

• Bug fix (non-breaking change which fixes an issue)

Double Check

• [X] I have read the comments and followed the CONTRIBUTING.md.
• [X] I have explained my PR according to the information in the comments or in a linked issue.
• [X] My PR source branch is created from the develop branch.
• [X] My PR targets the develop branch.
• [X] All my commits have --signoff applied