nvmf_tcp: Avoid unsigned arithmetic overflow for data lengths in PDUs

[jhb]

Summary

When evaluating the data offset and data length fields in C2HData and
H2CData PDUs, validate the data offset against the maximum valid value
relative to the supplied data length before adding the two values
together.

For R2T PDUs, validate the supplied data length against the maximum
valid value relative to the supplied data offset. In this case,
data_offset is already known to be equal to cb->data_xfered which is
always less than cb->data_len.

Reported by: Yehyeong Lee <[e-mail]> (R2T overflow)
Sponsored by: Chelsio Communications