android/client: Use memcpy() for getting CMSG_DATA()

This is how it is done in all other places in BlueZ. Also drop
unnecessary "descs" local variable.

Fixes clang error:

android/client/if-sock.c:164:11: error: cast from 'unsigned char *' to
'int *' increases required alignment from 1 to 4 [-Werror,-Wcast-align]