package/linphone: bump to version 4.4.8

package/linphone: bump to version 4.4.8

Set GIT_EXECUTABLE to OFF to avoid the following build failure:

CMake Error at /home/fabrice/br-test-pkg/br-arm-cortex-a9-glibc/host/arm-buildroot-linux-gnueabihf/sysroot/usr/share/bctoolbox/cmake/bctoolboxCMakeUtils.cmake:162 (message):
  invalid git describe version: ''
Call Stack (most recent call first):
  CMakeLists.txt:125 (bc_compute_lib_version)

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>