audit: filter PATH records keyed on filesystem magic

audit: filter PATH records keyed on filesystem magic

Tracefs or debugfs were causing hundreds to thousands of PATH records to
be associated with the init_module and finit_module SYSCALL records on a
few modules when the following rule was in place for startup:
	-a always,exit -F arch=x86_64 -S init_module -F key=mod-load

Provide a method to ignore these large number of PATH records from
overwhelming the logs if they are not of interest.  Introduce a new
filter list "AUDIT_FILTER_FS", with a new field type AUDIT_FSTYPE,
which keys off the filesystem 4-octet hexadecimal magic identifier to
filter specific filesystem PATH records.

An example rule would look like:
	-a never,filesystem -F fstype=0x74726163 -F key=ignore_tracefs
	-a never,filesystem -F fstype=0x64626720 -F key=ignore_debugfs

Arguably the better way to address this issue is to disable tracefs and
debugfs on boot from production systems.

See: https://github.com/linux-audit/audit-kernel/issues/16
See: https://github.com/linux-audit/audit-userspace/issues/8
Test case: https://github.com/linux-audit/audit-testsuite/issues/42

Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
[PM: fixed the whitespace damage in kernel/auditsc.c]
Signed-off-by: Paul Moore <paul@paul-moore.com>