Defines starting with `n' in kern

• NA kern/tty.c:84
• NCL_INIT kern/uipc_mbuf.c:59
• NFS_VFSOPS kern/vfs_conf.c:83
• NL kern/tty.c:87
• NO kern/tty.c:83
• NPTY kern/tty_pty.c:55
• NTBS kern/tty_tb.c:94
• NULL_VFSOPS kern/vfs_conf.c:111