1. In order to remove any SMACK extended attribute from a file, a user
should have CAP_MAC_ADMIN capability. But user without having this
capability is able to remove SMACK64MMAP security attribute.

2. While validating size and value of smack extended attribute in
smack_inode_setsecurity hook, wrong error code is returned.
Signed-off-by: NPankaj Kumar <pamkaj.k2@samsung.com>
Signed-off-by: NHimanshu Shukla <himanshu.sh@samsung.com>