[XFRM]: Assorted IPsec fixups

This patch fixes a number of small but potentially troublesome things in the
XFRM/IPsec code:

 * Use the 'audit_enabled' variable already in include/linux/audit.h
   Removed the need for extern declarations local to each XFRM audit fuction

 * Convert 'sid' to 'secid' everywhere we can
   The 'sid' name is specific to SELinux, 'secid' is the common naming
   convention used by the kernel when refering to tokenized LSM labels,
   unfortunately we have to leave 'ctx_sid' in 'struct xfrm_sec_ctx' otherwise
   we risk breaking userspace

 * Convert address display to use standard NIP* macros
   Similar to what was recently done with the SPD audit code, this also also
   includes the removal of some unnecessary memcpy() calls

 * Move common code to xfrm_audit_common_stateinfo()
   Code consolidation from the "less is more" book on software development

 * Proper spacing around commas in function arguments
   Minor style tweak since I was already touching the code

Signed-off-by: Paul Moore <paul.moore@hp.com>
Acked-by: James Morris <jmorris@namei.org>
Signed-off-by: David S. Miller <davem@davemloft.net>