Defines starting with `n' in kern

• NA kern/tty.c:84
• nch_back kern/vfs_cache.c:71
• nch_forw kern/vfs_cache.c:70
• NCL_INIT kern/uipc_mbuf.c:57
• NL kern/tty.c:87
• NO kern/tty.c:83
• NPTY kern/tty_pty.c:56
• NTBS kern/tty_tb.c:94