keepalived: add indent param in config_section_open/close

keepalived: add indent param in config_section_open/close

Add a parameter for indent in config_section_open and
config_section_close. Previously you had to separately add indents
while parsing if a section was inside another section.
Now this is supported by these two functions.
You can specify how much indent you need to add before opening or closing
a section.

Signed-off-by: Rishabh <redacted>