misc: reduce struct and struct field sizes

misc: reduce struct and struct field sizes

- by using BIT() instead of bool
- imap: shrink struct
- ftp: make state 'unsigned char'
- ftp: sort ftp_conn struct entries on size
- urldata: use smaller fields for SSL version info storage
- pop3: reduce the pop3_conn struct size
- smtp: reduce the size of the smtp structs

Closes #10186