netutils/libshvc: implement headers export and update shv-libs4c

[ppisa]

Summary

The uLUt and libshvc declare headers intended for make export by EXPORTED_INCLUDES mechanism implemented during 2026 Micowindows GSoC. The shv-libs4c has been updated as well to support newer pyshv versions and that way firmware updates when shv-nxboot-updater is used through pyshv based shvflasher.py and related GUI.

For pyshv see https://github.com/silicon-heaven/pyshv

New commits from shv-libs4c project

https://github.com/silicon-heaven/shv-libs4c

• shv_com_common: shv_unpack_discard and shv_unpack_skip

  required to skip additional parameters and query requests
  introduced introduced by newer silicon-heaven protocol
  and pyshv. Incorrect skipping was a bug even against
  previous protocol version but did not present itself because
  older pyshv did not send additional requests which need
  to be ignored.

• shv_file_node: small, but crucial unpack change

  Ignore any other messages than PARAM in file node's write unpack
  function. Other different states should be handled, too.

• shv_file_node: fix the CRC unpack method too

  Any other messages than PARAM are ignored.

• shv_com: add a method to close a connection only

• shv_dotdevice_node.c: close the conn with the other side when resetted

• shv_com.h: use array designators for error strings

• libshvtree: move shv_con_errno_strs to the C file to not waste space by copies

• shvtree/shv_clayer_posix: provide alternative socketpair notification support

  This allows to use shv-libs4c and related pysimCoder support on RTEMS system which does not provide functional pipe directive/system call but BSD networking supported local/UNIX socket pair is fully supported.

Impact

The update fixes shv-nxboot-updater to work when latest pyshv is used with NuttX included scripts

https://github.com/apache/nuttx-apps/tree/master/examples/shv-nxboot-updater/update-script

and allows to use SHV from NuttX build from applications build against NuttX export.

Testing

Only build and make export has been examined at this time, but newer shv-libs4c is used and was crucial update for https://github.com/robertobucher/pysimCoder delivery to https://utia.cas.cz/en/ in December 2025 and it has been used there from pysimCoder with NuttX export without SHV enabled (it would not work with pysimCoder due missing EXPORTED_INCLUDES ). Newer shv-libs4c version has been used locally updated NuttX builds of minimal image with shv-nxboot-updater from that time as well. It is time to move forward, as EXPORTED_INCLUDES is implemented and integrated into NuttX mainline.

[ppisa]

Note to inform @zdebanos, @michallenc, @Cynerd, @robertobucher about NuttX libshvc update and solved headers export.