modem: ublox-sara-r4: do not truncate outgoing datagrams
modem: ublox-sara-r4: do not truncate outgoing datagrams

Do not truncate outgoing datagrams if they do not fit in maximum handled
packet size. Set EMSGSIZE errno and return -1 instead.

Signed-off-by: Marcin Niestroj <63506c06cfbc47ace147db1702f6e751f5ac2132@emb.dev>

zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr