net: tcp: Removed copy of conn->unacked_len
net: tcp: Removed copy of conn->unacked_len

In the function tcp_send_data, the variable conn->unacked_len in copied
into a local variable pos. This value is only used in one location and
used mixed with the original conn->unacked_len.

This fix removes pos and switches to use conn->unacked_len everywhere
to reduce the chance of confusion. This does not functionally change the
code.

Signed-off-by: Sjors Hettinga <93f56ef9e57f8484e3a64ae8e636884690efc303@gmail.com>

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