tools: Handle deletes of entire interface context as deleting each line

tools: Handle deletes of entire interface context as deleting each line

Ticket: CM-14260
Reviewed By: CCR-14260
Testing Done: quagga reload tests (quagga_service, bgp_enhe etc.)

Quagga reload handles deletes of entire context by issuing a "no.." on the
entire context itself instead of deleting each individual line of the context.
However, this doesn't work when the context is "interface" since its not
allowed to do "no interface <ifname>" inside quagga. So special case this by
deleting each individual line of the context.

Signed-off-by: Dinesh Dutt <ddutt@cumulusnetworks.com>