If CONFIG_CIFS_WEAK_PW_HASH is not set, CIFSSEC_MUST_LANMAN
and CIFSSEC_MUST_PLNTXT is defined as 0.

When setting new SecurityFlags without any MUST flags,
your flags would be overwritten with CIFSSEC_MUST_LANMAN (0).
Signed-off-by: Niklas Cassel <niklass@axis.com>
Signed-off-by: Steve French <steve.french@primarydata.com>