doc: release_notes: add 4.2.1 release notes

Add 4.2.1 release notes, summarizing the issues addressed since 4.2 was
released.

Signed-off-by: Daniel DeGrasse <[email protected]>

Author: danieldegrasse

doc/releases/release-notes-4.2.rst

@@ -26,6 +26,57 @@
 
 .. _zephyr_4.2:
 
+.. _zephyr_4.2.1:
+
+Zephyr 4.2.1
+############
+
+This is a bugfix release for Zephyr 4.2.0. The following issues are addressed by this release:
+
+* :github:`96197` gPTP sample does not boot with NUCLEO-H563ZI
+* :github:`92393` LIS2DUX12 setting incorrect ODR configuration
+* :github:`93011` stm32u0: interrupt vectors for lpuart1 and lpuart2 are wrong in device tree
+* :github:`93220` Twister tests with coverage enabled crash during startup
+* :github:`93265` Stm32u5x: clock disable in sleep mode fix causing USB HS device initialization stalls
+* :github:`93342` doc: Documentation issue in 'connectivity/networking/api/tftp'
+* :github:`93350` net: tcp: keep-alive "pings" are no longer acknowledged with v4.2.0
+* :github:`93364` tests/subsys/llext fails after tagging 4.2
+* :github:`93424` Missing break after IPV6_MULTICAST_IF option processing
+* :github:`93445` STM32U535/545: dtc error for node wkup-pin@8 referencing non-existent port gpiof
+* :github:`93519` drivers: nxp_lpspi: Large performance degradation
+* :github:`93594` Nicla Vision has bad I2C address for VL53L1X sensor
+* :github:`93611` doc: Documentation issue in 'releases/release-notes-4.2'
+* :github:`93790` drivers: console: posix_arch_console: build warning with ``CONFIG_PRINTK=n``
+* :github:`93792` USB samples not working on ``max32690evkit``
+* :github:`93831` drivers: can: nrf: fix invalid pointer leading to undef behavior
+* :github:`93839` I3C: STM32: Has a Mutex deadlock on DAA Failure
+* :github:`94000` EXT2 fs_stat on mount point fails with a NULL pointer dereference.
+* :github:`94047` Shell device name tab completion for regulator parents show incorrect names
+* :github:`94063` SPI loopback tests failing on MAX32 SoCs.
+* :github:`94083` stm32:  u3:  low clock frequency for the RNG periphera
+* :github:`94093` Build error when OCRAM node is disabled in device tree (status = "disabled") [NXP RT1061]
+* :github:`94107` ppp link-layer address configuration is wrong
+* :github:`94325` iar: incorrect assembler optimzation flag
+* :github:`94473` LVGL Widgets Demo stopped working in v4.1 on mimxrt1060_evk@A
+* :github:`94702` Locally Administered Address (LAA) bit missing for STM32 ethernet driver
+* :github:`94703` Locally Administered Address (LAA) bit set on wrong index for NXP i.MX ethernet driver
+* :github:`94774` modules/picolibc: Roll back unnecessary changes, synchronize with SDK 0.17.4
+* :github:`94812` ``nocache`` data is included in ROM section
+* :github:`94842` iar: Zephyr 4.2 fails with IAR EWARM 9.70.1
+* :github:`94954` Spurious error log "No valid legacy adv to resume" in bt_hci_le_enh_conn_complete when using bt_le_ext_adv_start()
+* :github:`95113` gpio_pin_get_config for STM32 returns wrong flags value for input pins
+* :github:`95146` i2c: stm32: non-RTIO driver fixes on PM and on STM32F7 from Zephyr v4.3
+* :github:`95297` Links to the pyOCD repository are outdated
+* :github:`95456` Zephyr Netstack buffer leaks
+* :github:`95580` Picolibc module and SDK are not in sync for Zephyr 4.2.0
+* :github:`95721` Boards documentation: "arm" Architecture not specified at least for STM32MP13 and STM32N6 boards
+* :github:`95724` drivers: i2c: stm32: build error when using DMAs with st,stm32-i2c-v2 driver
+* :github:`95768` Possible TCP connection leak when creating a socket
+* :github:`95850` Applications do not watch MCUboot key file for changes
+* :github:`96087` TCP connection sends an incorrect seqnum FIN message
+* :github:`96172` arch: arm: switch to privilege stack in SVC handler
+* :github:`96768` incorrect i2c3 base address on stm32f303Xe
+
 Zephyr 4.2.0
 ############