Fix smbfs to not zero out statfs f_flags field. Previously, this
made getmntinfo() return empty flags for smbfs filesystems when
called with MNT_WAIT. It's not visible with mount(8), since it uses
MNT_NOWAIT, but broke autounmount(8) operation.

PR:		195161
Differential Revision:	https://reviews.freebsd.org/D1194
Reviewed by:	kib@
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation