net: sockets: Simplify if logic in sendto(), fix warning
net: sockets: Simplify if logic in sendto(), fix warning

send()/sendto() aren't "front facing" functions, so when user calls
them, context type hopefully should be already validated by other
functions. They are also on critical path of app/network performance,
so getting rid of extra check helps a little bit too. This also
fixes a warning of "err" possibly being used non-initialized.

Signed-off-by: Paul Sokolovsky <35cb557f011771c94f127d6fef99f804b62203f5@linaro.org>

explora26/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,aceofall/zephyr-iotos,punitvara/zephyr,zephyriot/zephyr,kraj/zephyr,finikorg/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,explora26/zephyr,galak/zephyr,finikorg/zephyr,Vudentz/zephyr,fbsder/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,zephyriot/zephyr,aceofall/zephyr-iotos,mbolivar/zephyr,galak/zephyr,ldts/zephyr,aceofall/zephyr-iotos,zephyrproject-rtos/zephyr,ldts/zephyr,punitvara/zephyr,Vudentz/zephyr,ldts/zephyr,nashif/zephyr,punitvara/zephyr,GiulianoFranchetto/zephyr,fbsder/zephyr,fbsder/zephyr,fbsder/zephyr,Vudentz/zephyr,kraj/zephyr,kraj/zephyr,zephyriot/zephyr,finikorg/zephyr,punitvara/zephyr,aceofall/zephyr-iotos,ldts/zephyr,kraj/zephyr,galak/zephyr,mbolivar/zephyr,aceofall/zephyr-iotos,zephyriot/zephyr,mbolivar/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,galak/zephyr,fbsder/zephyr,kraj/zephyr,nashif/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,nashif/zephyr,mbolivar/zephyr,punitvara/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,zephyriot/zephyr,zephyrproject-rtos/zephyr,mbolivar/zephyr,Vudentz/zephyr,galak/zephyr