net: make the sendmsg param type consistent with posix specification

[extinguish]

Summary

Update the sendmsg() socket API and its relative functions to use const-qualified message header parameters, aligning the implementation with the POSIX specification.

Impact

Improves API compliance with the POSIX standard, which defines sendmsg() as taking a const struct msghdr *

Testing

Verified that existing code compiles without warnings or errors after the change

[simbit18]

hi @extinguish this error has occurred.

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Configuration/Tool: photon/adb,CONFIG_ARM_TOOLCHAIN_GNU_EABI
2026-01-13 10:23:22
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  Cleaning...
  Configuring...
  Disabling CONFIG_ARM_TOOLCHAIN_GNU_EABI
  Enabling CONFIG_ARM_TOOLCHAIN_GNU_EABI
  Building NuttX...
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  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed

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100 44130  100 44130    0     0   162k      0 --:--:-- --:--:-- --:--:--  162k

100 1646k  100 1646k    0     0  5591k      0 --:--:-- --:--:-- --:--:-- 5591k
chip/stm32_gpio.c:44:11: note: '#pragma message: CONFIG_STM32_USE_LEGACY_PINMAP will be deprecated migrate board.h see tools/stm32_pinmap_tool.py'
   44 | #  pragma message "CONFIG_STM32_USE_LEGACY_PINMAP will be deprecated migrate board.h see tools/stm32_pinmap_tool.py"
      |           ^~~~~~~
Error: libuv/src/unix/nuttx.c:225:9: error: conflicting types for 'sendmsg'; have 'ssize_t(int,  struct msghdr *, int)' {aka 'int(int,  struct msghdr *, int)'}
  225 | ssize_t sendmsg(int sockfd, struct msghdr *msg, int flags) {
      |         ^~~~~~~
In file included from /github/workspace/sources/apps/system/libuv/libuv/include/uv/unix.h:30,
                 from /github/workspace/sources/apps/system/libuv/libuv/include/uv.h:71,
                 from libuv/src/uv-common.h:35,
                 from libuv/src/unix/internal.h:25,
                 from libuv/src/unix/nuttx.c:26:
/github/workspace/sources/nuttx/include/sys/socket.h:465:9: note: previous declaration of 'sendmsg' with type 'ssize_t(int,  const struct msghdr *, int)' {aka 'int(int,  const struct msghdr *, int)'}
  465 | ssize_t sendmsg(int sockfd, FAR const struct msghdr *msg, int flags);
      |         ^~~~~~~
make[2]: *** [/github/workspace/sources/apps/Application.mk:239: nuttx.c.github.workspace.sources.apps.system.libuv.o] Error 1
make[2]: Target 'all' not remade because of errors.
make[1]: *** [Makefile:54: /github/workspace/sources/apps/system/libuv_all] Error 2
make[1]: Target 'all' not remade because of errors.
make: *** [tools/LibTargets.mk:248: /github/workspace/sources/apps/libapps.a] Error 2
make: Target 'all' not remade because of errors.
/github/workspace/sources/nuttx/tools/testbuild.sh: line 385: /github/workspace/sources/nuttx/../nuttx/nuttx.manifest: No such file or directory
  [1/1] Normalize photon/adb
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