devlink: fix grammar and style issues in man pages

This patch addresses various grammatical errors, style inconsistencies,
and clarity issues across the devlink man page documentation.

Changes by file:

devlink.8:
  - Add missing article "The" in -b option description
  - Add missing periods in object descriptions (region, health, trap)
  - Update synopsis to include all objects (rate, lc, dpipe)
  - Add descriptions for rate, lc, and dpipe objects
  - Add complete cross-references in SEE ALSO section

devlink-dev.8:
  - Change "HWs" to "hardware devices" for clarity
  - Fix verb form: "restart driver" -> "restarting the driver"
  - Fix plural agreement: "some driver" -> "some drivers"
  - Fix typo: "actrually" -> "actually"

devlink-port.8:
  - Capitalize "Set port type" parameter description
  - Fix preposition: "split to" -> "split into"
  - Fix punctuation: "on. or" -> "on, or"
  - Rewrite pfnum description for grammatical clarity
  - Fix plural agreement: "devices which supports" -> "devices which support"
  - Fix article: "a Ethernet" -> "an Ethernet"
  - Fix verb form: "restart driver" -> "restarting the driver"
  - Fix typo: "Unplit" -> "Unsplit"
  - Fix verb form: "active the function" -> "activate the function"

devlink-rate.8:
  - Fix plural agreement: "some driver" -> "some drivers"
  - Fix possessive pronouns: "it's" -> "its" (3 instances)
  - Fix plural: "leaf have" -> "leaves have"
  - Add article: "create leaf rate object" -> "create a leaf rate object"
  - Format "1to1" as "1-to-1"
  - Fix plural: "These parameter" -> "These parameters"
  - Add verb: "parent node applied" -> "parent node are applied"
  - Fix spelling: "behaviour" -> "behavior"
  - Improve phrasing: "treated as parent unset" -> "is treated as unsetting the parent"

No functional changes. All technical content remains accurate.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David Ahern <dsahern@kernel.org>