bgpd: convert network statements from DEFUN to DEFPY

bgpd: convert network statements from DEFUN to DEFPY

Problems reported with inconsistent use of parameters for bgp network
statements.  Converted 12 DEFUNs to 2 DEFPY statements, making the
parameter use consistent with the exception of keeping the "backdoor"
keywork ipv4 only.  Also verified that if a route-map or label-index
is specified in the "no" case it matches what had been previously
defined. Manual testing looks good and bgp-smoke will be performed
before pushing.

Ticket: CM-16860
Signed-off-by: Don Slice <dslice@cumulusnetworks.com>
Reviewed-by: CCR-7056