The values are parsed as u16/u32, but kernel limits allowed values.
Signed-off-by: Phil Sutter <phil@nwl.cc>
.BR 4 " (blocking)."
.BI priority " PRIO"
-- set port priority (a 16bit unsigned value).
+- set port priority (allowed values are between 0 and 63, inclusively).
.BI cost " COST"
-- set port cost (a 32bit unsigned value).
+- set port cost (allowed values are between 1 and 65535, inclusively).
.BR guard " { " on " | " off " }"
- block incoming BPDU packets on this port.