Turn to Halliwell's Dictionary of Archaic and Provincial Words, 2d edition, and there is this explanation:—
"SNECK, that part of the iron fastening of a door which is raised by moving the latch. To sneck a door, is to latch it."
See also Burn's Poems: The Vision, Duan First, 7th verse, which is as follows:—
"When dick! the string the snick did draw,—
And jee! the door gaed to the wa';
An' by my ingle-lowe I saw,
Now bliezin' bright,
A tight, outlandish Hizzie, braw,
Come full in sight."
These quotations will clearly show that "sneck" or "snick" applies to a door; and that to sneck a door is to shut it. I think, therefore, that Sir Toby meant to say in the following reply:—