[debuglog] Migrate to zx_debuglog_create

Test: cq

Change-Id: Ia7aa2efefd0c1ac0ce3460159a9405d6f0b1777e

[clock] zx_clock_get(ZX_CLOCK_MONOTONIC) -> zx_clock_get_monotonic()

Test: no functional change

Change-Id: Iaa513c521d96b178458acc707be3646067971701

[logging] Migrate zircon off zx_log_read and zx_log_write

zx_log_create is trickier. It's essentially a version of
zx_debuglog_create that allows not passing a root resource.

ZX-2184

Change-Id: Ida3d6bacce2c4601a4c6a00fd0cf13c902eb1d41

[netsvc] Reduce debuglog send rate when noone is listening

Tested by killing loglistener and watching send rate via tcpdump.

ZX-1904 #done

Change-Id: I5af76e04ad634bc53acd52b3b9614237d784e2c9

[syscalls] Rename zx_time_get to zx_clock_get

This change frees up the get() method in for a zx_time_t accessor in the
zx::time class.

Change-Id: Ia4cdc7e3e558df5ba0cfeedb27a442abf4d6f305

[netsvc] [inet6] Allow send operations to block

Add block option to {udp|icmp}6_send functions so the caller can chose
to wait if FIFO tx buffers are unavailable.

Change-Id: Ic3f40f41970d75e2cd3fd9b125d94937f6c521a3

[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[debuglog][mxio][devhost] tidy up log flags, introduce local

- remove old subsystem identity flag values
(subsystems will return later in a better way)
- pull standard log flag definitions into syscalls/log.h
- introduce new LOCAL flag
- introduce DDK_LOG_L* variants
- pass flags through dprintf() to log write
- only filter on level flags

Change-Id: Ibeba1b27e9cfc543b441965414f2651ddfc749aa

[bootloader][netsvc][libtftp] Add timeout support

Add libtftp support for timeout handing as per TFTP RFC. Also,
sets a limit for the number of consecutive timeouts before a
connection is terminated (configurable using
tftp_set_max_timeouts()).

Change-Id: I9a31605d6f926275afdc32fbd8dbcab141ccc993

[netsvc] Refactor debuglog support

Move debuglog support into a separate compilation unit. This should
simplify things quite a bit when adding another timeout source (tftp).

Also, give a name to the debuglog magic number (NB_DEBUGLOG_MAGIC).

Change-Id: Id47f6503cb74cbfb535326d60993daf4b128befd