mount: Fix bug regarding not honored ACL

This commit fixes problem with not honored ACLs. Providing
FUSE_CAP_POSIX_ACL capability flag (that was defined in libfuse 3.2.0)
solves the problem for mfsmount3 but not for mfsmount because
FUSE_CAP_POSIX_ACL is defined only in FUSE3 mount_config.h header file.
Removing default_permissions from default mount options would solve the
problem for both mfsmount and mfsmount3 but it would introduce another
one: unprivileged users would be able to elevate their privileges with
setfacl.

Fixes #816

Change-Id: If34502b5ec1b7e2df3eb9fcbbcb35b91a3c3b6f0

src/mount/fuse/main.cc

@@ -120,6 +120,7 @@ static void mfs_fsinit(void *userdata, struct fuse_conn_info *conn) {
 #if FUSE_VERSION >= 30
 	fuse_conn_info_opts *conn_opts = (fuse_conn_info_opts *)userdata;
 	fuse_apply_conn_info_opts(conn_opts, conn);
+	conn->want |= FUSE_CAP_POSIX_ACL;
 	conn->want &= ~FUSE_CAP_ATOMIC_O_TRUNC;
 #endif