FreeSWITCH-FS-7269

ss7: adding ss7_iam_fwd_ind_hex as x-header and channel variables in hex format.
     Read the forward call indicator IE and print it into channel variable
     ss7_iam_fwd_ind_hex. If this variable exists, put it in the x-header.
     This implementation takes bits of A, CB, D, E, F, HG, I from the hex
     value. Bits of KJ, L, P-M are not taken and set to 0.
     The hex value is H-A-P-I, H is the highest bit to A, and next is P-I.
     I is the lowest bit in the whole field, and H is the highest bit in
     the whole field. Refer to Q.763 chapter 3.23.