mausezahn: Fix reading of hex payload file
Using the option -F with mausezahn, to read input out of a hexfile,
results in corrupt data transmitted (first byte will always be 0).
Properly parse "payload="/p=" at the start of the file by the same
method as used in layer3.c and layer4.c
Closes #153
Reference: http://permalink.gmane.org/gmane.linux.network.netsniff-ng/600
Signed-off-by: Thomas Fleischmann <thomas.fleischmann.08@googlemail.com>
Reported-by: Thomas De Schampheleire
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>