Fix fcntl F_GETFL F_SETFL for files opened execute-only (O_EXEC).

The FFLAGS and OFLAGS now work correctly also for files opened with O_EXEC.
Except possibly fuse, the other users pass values without O_EXEC set. fuse
appears to assume O_EXEC is handled correctly.

Although F_SETFL may not be commonly used for execute-only file descriptors,
F_GETFL may be useful to find the access mode.
Implement the ip, tcp, and udp DTrace providers. The probe definitions use
dynamic translation so that their arguments match the definitions for
these providers in Solaris and illumos. Thus, existing scripts for these
providers should work unmodified on FreeBSD.

Tested by:	gnn, hiren
MFC after:	1 month