lockdown: Print current->comm in restriction messages

Print the content of current->comm in messages generated by lockdown to
indicate a restriction that was hit.  This makes it a bit easier to find
out what caused the message.

The message now patterned something like:

	Lockdown: <comm>: <what> is restricted; see man kernel_lockdown.7

Signed-off-by: David Howells <dhowells@redhat.com>