Eliminate incorrect and unnecessary check for changed IP address
    
    Commit aa2cc7 modified a previously unnecessary but innocuous check
    for interface IP address during interface update incorrectly, causing
    all attempted updates (e.g. changing link state) to interfaces of
    type='ethernet' for QEMU to fail.
    
    This patch fixes the issue by completely removing the check for IP
    address, which is pointless since QEMU doesn't support setting
    interface IP addresses from the domain interface XML anyway.
    
    Signed-off-by: Vasiliy Tolstov <v.tolstov@selfip.ru>
    Signed-off-by: Laine Stump <laine@laine.org>