pcap_setdirection - set the direction for which packets will be captured
int pcap_setdirection(pcap_t *p, pcap_direction_t d);
pcap_setdirection() is used to specify a direction that packets will be
captured. d is one of the constants PCAP_D_IN, PCAP_D_OUT
or PCAP_D_INOUT. PCAP_D_IN will only capture packets received by
the device, PCAP_D_OUT will only capture packets sent by the device and
PCAP_D_INOUT will capture packets received by or sent by the device.
PCAP_D_INOUT is the default setting if this function is not called.
pcap_setdirection() isn't necessarily fully supported on
all platforms; some platforms might return an error for all values, and some
other platforms might not support PCAP_D_OUT.
This operation is not supported if a ``savefile'' is being
pcap_setdirection() returns 0 on success and PCAP_ERROR on
failure. If PCAP_ERROR is returned, pcap_geterr(3PCAP) or
pcap_perror(3PCAP) may be called with p as an argument to fetch
or display the error text.