Fix cisco_ios show lldp neighbors blank-capability parsing

[olasupo]

Fixes #2327

Problem

cisco_ios_show_lldp_neighbors mis-parses a neighbor row when the Capability column is blank and the Port ID contains a space (for example Port 6). Because CAPABILITIES was (\S*), it greedily consumed the first word of the Port ID:

Raw row	Parsed (before)
ABC-Ultra-210W Gi2/0/16 110 <blank> Port 6	capabilities="Port", neighbor_interface="6"

A blank-capability row whose Port ID is a single token (e.g. Gi0/1 or a MAC) already parsed correctly — only multi-word Port IDs were affected. Reported against a WS-C3750X running 15.0(2)SE10a.

Fix

• Constrain CAPABILITIES to the documented LLDP capability-code letters ([BRCWPSTO,]+) and make the field optional. It can no longer match a Port ID word such as Port, because the lowercase continuation breaks the match while the capability codes are always uppercase.
• Allow NEIGHBOR_INTERFACE to hold a multi-word Port ID.

After the fix the same row parses as capabilities="", neighbor_interface="Port 6".

Tests

Added cisco_ios_show_lldp_neighbors3.raw/.yml from the reporter's capture, covering blank capabilities with single-word, multi-word (Port 6) and MAC-address Port IDs, plus normal and multi-code (B,R) rows. The two existing fixtures are unchanged and still pass, and the full test suite passes.

[matt852]

Recommendation: Changes Suggested

Breaking Change: No

Thanks @olasupo. This is a clean fix with great fixture coverage of the blank-capability edge cases. One suggestion before merge:

• Add ^. -> Error termination (and the supporting header/blank-line rules) to both states. Our parser conventions ask that each state end with ^. -> Error so every line of raw output is accounted for, and since this PR already reworks both LLDP rules it's a natural moment to bring the template up to convention. In ntc_templates/templates/cisco_ios_show_lldp_neighbors.textfsm, the Start state:

   Start
     ^Device.*ID -> LLDP
     # Capture time-stamp if vty line has command time-stamping turned on
     ^Load\s+for\s+
     ^Time\s+source\s+is
  +  ^Capability codes:
  +  ^\s+\(
  +  ^\s*$$
  +  ^. -> Error

  And the LLDP state (the ^Total\s+entries\s+displayed and ^\s*$$ rules must sit above the ^${NEIGHBOR_NAME} rule, which otherwise matches nearly any line):

   LLDP
     ^${NEIGHBOR_NAME}\s*${LOCAL_INTERFACE}\s+\d+\s+(?:${CAPABILITIES}\s+)?${NEIGHBOR_INTERFACE}\s*$$ -> Record
  +  ^Total\s+entries\s+displayed
  +  ^\s*$$
     ^${NEIGHBOR_NAME}
     ^\s+${LOCAL_INTERFACE}\s+\d+\s+(?:${CAPABILITIES}\s+)?${NEIGHBOR_INTERFACE}\s*$$ -> Record
  +  ^. -> Error

  All existing and new fixtures pass unchanged with these additions.