cifs: fix interface count calculation during refresh

The last fix to iface_count did fix the overcounting issue.
However, during each refresh, we could end up undercounting
the iface_count, if a match was found.

Fixing this by doing increments and decrements instead of
setting it to 0 before each parsing of server interfaces.

Fixes: 096bbeec

 ("smb3: interface count displayed incorrectly")
Cc: stable@vger.kernel.org # 6.1
Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>