SMTP: Store correct password into the password manager

The configuration ties the SMTP account with the IMAP account (in terms
of per-profile access), so it was wrong to use the default account name.
This fixes a rare configuration where the user is:

• using a non-default profile,
• requires SMTP auth,
• *and* uses a different set of credentials for SMTP access compared to IMAP.

Change-Id: Id6d341d14bf795943d8f3b7b42fac587a062141d