selinux: remove redundant selinux_nlmsg_perm

selinux_nlmsg_perm is used for only by selinux_netlink_send. Remove
the redundant function to simplify the code.

Fix a typo by suggestion from Stephen.

Signed-off-by: Huaisheng Ye <yehs1@lenovo.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <paul@paul-moore.com>