sd-bus: avoid magic number in SASL length calculation
    
    Lets avoid magic numbers and use a constant `strlen()` instead.
    
    Signed-off-by: David Rheinsberg <david.rheinsberg@gmail.com>
    (cherry picked from commit 3cacdab925c40a5d9b7cf3f67719201bbaa17f67)
    
    Related: #1838081
    
    patch_name: 0400-sd-bus-avoid-magic-number-in-SASL-length-calculation.patch
    present_in_specfile: true
    location_in_specfile: 400
    squash_commits: true