smf_method(5): fix description of security_flags

*** 313,325 ****
             security-flags(5).
  
  
             The "default" keyword specifies those flags specified in
             svc:/system/process-security.  The "all" keyword enables all flags,
!            the "none" keyword enables no flags.  Further flags may be added by
!            specifying their name, or removed by specifying their name prefixed
!            by '-' or '!'.
  
  
             Use of "all" has associated risks, as future versions of the system
             may include further flags which may harm poorly implemented
             software.
--- 313,326 ----
             security-flags(5).
  
  
             The "default" keyword specifies those flags specified in
             svc:/system/process-security.  The "all" keyword enables all flags,
!            the "none" keyword enables no flags.  The "current" keyword
!            specifies the current flags.  Flags may be added by specifying
!            their name (optionally preceded by '+'), and removed by preceding
!            their name with '-').
  
  
             Use of "all" has associated risks, as future versions of the system
             may include further flags which may harm poorly implemented
             software.