Fix dhcpcd startup when net.hostname is not set

Commit 62d6f748 swapped p2p_interface and DHCP_CONFIG_PATH
erroneously. This reverts them to their correct ordering and makes dhcpcd
startup work again.

Change-Id: Iea033a7e0dad98bb2a63fb39755330675cfbb0ab
Signed-off-by: Matt Gumbel <matthew.k.gumbel@intel.com>