Remove getenv from dal/dpdk/dal_init.c

[fruffy]

The P4 DPDK target tries to get the SDE install environment via an environment variable:

p4-dpdk-target/src/pipe_mgr/shared/dal/dpdk/dal_init.c

Line 107 in ea8ed80

install_dir = getenv("SDE_INSTALL");

This seems like it might easily lead to user errors or bugs. Is it possible to replace this call with a checked command line parameter?