Implement Flow Connection State about ntopng HOT 1 OPEN

Proposal:
Create an enum in the Flow class like the following:
Enum ConnectionState { NO_STATE, S0, S1, … }

In the Flow::updateTcpFlags method, a method named 'select_connection_state' will be called with parameters for the variables (src2dst_tcp_flags, dst2src_tcp_flags). The 'select_connection_state' method will select one of the states mentioned before by checking the current TCP flags in the src2dst_tcp_flags and dst2src_tcp_flags with the following logic:

S0: Only SYN in src2dst_tcp_flags; no flags in dst2src_tcp_flags
S1: 3whs ok and no FIN in src2dst_tcp_flags and no RST src2dst_tcp_flags
SF: 3whs and FIN src2dst_tcp_flags and FIN src2dst_tcp_flags
REJ: SYN in src2dst_tcp_flags and RST in dst2src_tcp_flags
S2: Was S1 and FIN in src2dst_tcp_flags and no FIN in dst2src_tcp_flags
S3: Was S1 and FIN in dst2src_tcp_flags and no FIN in src2dst_tcp_flags
RSTO: Was S1 and RST in src2dst_tcp_flags
RTSR: RST in dst2src_tcp_flags
RSTOS0: SYN and RST in src2dst_tcp_flags; no SYN+ACK in dst2src_tcp_flags
RSTRH: SYN+ACK and RST in dst2src_tcp_flags; no SYN in src2dst_tcp_flags
SH: SYN and FIN in src2dst_tcp_flags; no SYN+ACK in dst2src_tcp_flags
SHR: SYN+ACK and FIN in dst2src_tcp_flags; no SYN in src2dst_tcp_flags
OTH: NO SYN in src2dst_tcp_flags and NO SYN in dst2src_tcp_flags

After the selection of the connection state, the 'select_connection_state' method will update the new variable of the Flow class ConnectionState currentConnectionState.

from ntopng.