Switch from stable-4.2 branch to upstream v4.6.1 release + fixes.

## [Unreleased]

### Fixed

 - Haiku fixes. !98 !99
 - Fix a minor DHCP regression introduced in 4.6.0. !97

## [4.6.1] - 2021-06-18

### Fixed

 - Fix DHCP regression introduced in 4.6.0. !95

## [4.6.0] - 2021-06-14

### Added

 - mbuf: Add debugging helpers for allocation. !90

### Changed

 -  Revert "Set macOS deployment target to macOS 10.4". !93

### Fixed

 - mtod()-related buffer overflows (CVE-2021-3592 #44, CVE-2021-3593 #45,
   CVE-2021-3594 #47, CVE-2021-3595 #46).
 - poll_fd: add missing fd registration for UDP and ICMP
 - ncsi: make ncsi_calculate_checksum work with unaligned data. !89
 - Various typos and doc fixes. !88

## [4.5.0] - 2021-05-18

### Added

 - IPv6 forwarding. !62 !75 !77
 - slirp_neighbor_info() to dump the ARP/NDP tables. !71

### Changed

 - Lazy guest address resolution for IPv6. !81
 - Improve signal handling when spawning a child. !61
 - Set macOS deployment target to macOS 10.4. !72
 - slirp_add_hostfwd: Ensure all error paths set errno. !80
 - More API documentation.

### Fixed

 - Assertion failure on unspecified IPv6 address. !86
 - Disable polling for PRI on MacOS, fixing some closing streams issues. !73
 - Various memory leak fixes on fastq/batchq. !68
 - Memory leak on IPv6 fast-send. !67
 - Slow socket response on Windows. !64
 - Misc build and code cleanups. !60 !63 !76 !79 !84

## [4.4.0] - 2020-12-02

### Added

 - udp, udp6, icmp: handle TTL value. !48
 - Enable forwarding ICMP errors. !49
 - Add DNS resolving for iOS. !54

### Changed

 - Improve meson subproject() support. !53
 - Removed Makefile-based build system. !56

### Fixed

 - socket: consume empty packets. !55
 - check pkt_len before reading protocol header (CVE-2020-29129). !57
 - ip_stripoptions use memmove (fixes undefined behaviour). !47
 - various Coverity-related changes/fixes.

## [4.3.1] - 2020-07-08

### Changed

 - A silent truncation could occur in `slirp_fmt()`, which will now print a
   critical message. See also #22.

### Fixed

 - CVE-2020-10756 - Drop bogus IPv6 messages that could lead to data leakage.
   See !44 and !42.
 - Fix win32 builds by using the SLIRP_PACKED definition.
 - Various coverity scan errors fixed. !41
 - Fix new GCC warnings. !43

## [4.3.0] - 2020-04-22

### Added

 - `SLIRP_VERSION_STRING` macro, with the git sha suffix when building from git
 - `SlirpConfig.disable_dns`, to disable DNS redirection #16

### Changed

 - `slirp_version_string()` now has the git sha suffix when building form git
 - Limit DNS redirection to port 53 #16

### Fixed

 - Fix build regression with mingw & NetBSD
 - Fix use-afte-free in `ip_reass()` (CVE-2020-1983)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Doug Evans <dje@google.com>